I've been making mansions, because they're so amazingly complex to me and it's lots of fun, (I've started 5) but once I've gotten the exterior made, the landscaping done, and the rooms made, I find myself extremely unmotivated after I've furnished only a few rooms of each house. I don't enjoy building small houses as much.. and I like the challenge of the large exteriors, but once I've got a home with 6-10 bedrooms, I'll furnish one bedroom, a dining room, and a living area, and then be at a loss for the rest-- don't even get me started on bathrooms and those, unnecessary, hobby rooms that stereotypical mansions have (ex. music room, art studio, and basically every room found on a clue game board ). My questioned to seasoned (or even new but inspired) builders, how do you guys keep yourselves interested in a big build?

I've tried (with my five separate mansion creations) to keep them all different styles, and switch back and forth between them all-- there are 2 modern, one very traditional-like, a sort of in between, and then an abomination that I haven't decided on what its style should be (only the outside has style correlation, the inside is just a mess), but I'm still finding myself bored of them. I stick to base game furniture unless I absolutely have to stray- and I'm not willing to negotiate that, which could be one stem for my problem here (the repetition in furniture, in particular).

So anyway.. any tips from fellow builders to stay motivated?

I feel you absolutely. In this respect, even a 40x40 size lot is too big for me to build. (Luckily, I like small scales.) I always wonder how patient and dedicated those builders are who upload 64x64 mansions entirely furnished - I could never complete such a thing.
If I were you, maybe, it would worth a try, to imagine a different function or history for the building: technically, it would be a residential mansion with a household, of course, but inside, the interiors could radiate an alternate story-line, like for example, it was once a mansion of a rich family, but after they became extinct, the building was turned into a ... boarding school? museum? scientific research site? orphanage? artists' colony? dorm for a posh university? /insert any innovative idea here/
Of course it wouldn't make it a community lot, it would stay a residential for a group of sims, but mayyybee it would make it more interesting to furnish the rooms instead of the stereotypical clue game board.

I feel you too. I just leave rooms blank until I have that eureka moment. I have like 20 hoods in my "modern day" save game, so it can take years till I get round to it. Sometimes things you might not think of, like a gaming room or a study room, can fill that extra space. Don't force yourself, just have fun.

It also helps if you periodically go back to Edit Town, drop the current version of the lot into the Lots bin, and then go do something else for a while when you start getting bored. (Also handy as a way to cut your losses in case of a power outage, game crash, etc.) Then when you are feeling fresh again, you can drop the incomplete lot into the game, work on it some more, and drop it back in the bin when you are either finished or tired of working on it again.

I've found it surprisingly easy to do. I haven't built any large residential lots in a long, long time but the lots I'm building for my series are usually a blast to build and decorate. Once I have a basic shape everything kind of falls into place. Sure, the lack of appropriate items is always an issue and doubly so with the period factor but that's a game in and of itself.

Why not just leave the lot where it is instead of putting it in the lot bin?

I find for larger houses, slowly-growing, jumbled-together mansions that are built while you play a family are more fun to build than ones that are designed and built at once. You start off with a core, and then add wings around it over time.

Of course, landscaping will need to be sparser at first, but it's nice to see a house evolve (new baby? The house needs an orangery!) rather than feeling like you need to slavishly follow the original design.

It feels like the TS1 intro video, or the house drawings you make as a kid where you add more and more to it until it fills a page lol

That makes sense.. Usually I stop playing the actual game for months on end while just making buildings, and then when I play I'll play a family for a few weeks and not build a single thing-- probably not the best strategy for not getting bored haha.

But, hey, I love landscaping! I can't do sparse!

Because it's faster to drop the lot into the bin than it is to save the entire game.

I find having a klepto or two sims helps a lot. SO when I don't know what to put in a room I send them out stealing things, or see what they brought home from work. THen I make a room around the stuff the Sims dragged home. Sometimes you get things you didn't know where in the game like a giant sundae and a giant icecream cone. Ended up making a very colorful game room.

Normally when people show they rooms they point out to the cental items i.e. TVs, art etc. Your sims will go ... and here is the rubber duck I once "found" and I build the room around it!

You have the correct assumption... Did you know you can steal some plants? One palm plant has a glitch where you steal one palm plant you swipe EVERY one of the same kind the lot.

I'm doing a farming challenge since I have to restart my sims3 as whole. Since I screwed up I ended up to poor. You bet farming will go to building, but this thread I decided I will sell NOTHING I steal (well I can't anyways) and will build my properties around it. (I like doing multiple properties rather then one large it saves on lag that's why I ended up TO poor).

Nope, I did not know that! I have never really played with klepto sims. Seems like I need to try your playstyle. New building challenge: Use all the items you sims looted in one room. Have fun using 10 street lights in your kitchen.

IS that a challenge? Might be hard to find ten street lights, but I think someone challenged me.

My big issue with decorating large lots is usually scale. I'm terrible with filling up empty space and usually end up putting completely nonsensical things in or just building the same space 5-6 times over. Amber's mansion is mostly lounges. There's 3 living rooms, 4 lounges and two blacked out rooms I have no use for. It's way too large for a childless married couple in their late 20s. I gave them both a hobby room/home office but only ever used one. Eventually I had the bright idea to convert part of the house into a guest space, since there was only one usable bedroom in this massive mansion. I solved this by looking at the different architectural masses and giving each of them their own purpose.

(this is the part where I leave to take illustrative screenshots, only to realize the whole lot is still a giant mess, and I start to clean it up, and then the game crashes)

You can see it's still rough around the edges (it being 5 years old and all) but I've really been able to fill a few spaces in sensibly. Now this issue of mine is particularly relevant now that I've been building loads again for Bridgeport'88 but I can't show any of that until it's done.

I can so relate here. Building is one of my favorite things in the game but it’s always terrible when I just feel the ‘blahs’ on a house I’m working on.

Some things that keep me motivated are looking up inspiration pics online. Lots, and lots of inspiration pics. Pinterest and Google images are your best friend for inspo. Lol. I save the ones I especially love on my iPad and after looking at the pics for a while, I see different decorating techniques and styles that I’d like to incorporate in my houses. I’ve even taken to copying different textures I’ve seen from my inspiration pics and after going into CASt I can make the build in the game look really similar to the look in the pictures

Another thing I do is I simply stop working on the house that I get stuck on. If I don’t feel like decorating or anything then I either look up pics online for ideas or I just take a building break for a week or two until I actually feel like playing again. Lol.

Adding on to that, the last time I went to ikea had me building for hours. I took a bunch of pictures of the show floor for sim inspiration-- or.. simspiration. :D

HEre you go I've got some swiping and money issue but bare bones here. Some plants and rugs and I think we'd really be pulling it in here... But because of your challenge their kitchen is on a different island.

Hahaha and then there are just four treasure chests in a row. Gotta love what klepto sims decide to swipe lmao.

Na I bought those to store like fruits and what not so I don't accidentally sell them at the store. Certain there is a better way but I like doing it that way. Stoves on the other hand. That was a score, you realize how hard stoves are, never mind two identical ones! I tried stealing chests but you can't steal chests from tombs, and I never seen any townie with the other chests.

Wait, did he actually steal those street lights

Ohh that's a great idea! Sadly I don't have any Ikeas where I live but I should remember that for the other stores around here :D

Sims love to steal all kinds of lights! I had a sim who used to go to a lot that had a well-lit parking lot full of nice, expensive cars and every light was stolen before he even touched a car.

(He also stole all the lights from the art museum, and then complained that it was dark in there.)

I just keep going back and forth between project all the time. Some projects just falls through the cracks in the floor as well. I don't really bother too much about it. I have such a big production most usually, when it's time to select a subject for my blog, I have several to choose from.