I want a blank neighborhood/world where I can just build several houses at once. If I start a new game and bulldoze or delete everything there so I can just build will it affect other games that i was playing and saved? I usually switch between different games. Sorry if it's in the wrong spot.

Be sure to select SAVE AS and name it something like BUILDERS WORLD or something, so you can just load that particular game when you want it. Save your other games as well, naming them with unique names too! That way you can pick and choose.

No, you can do it safely. I have three saved games and every save maintains its own settings.
So, do not worry and demolish everything!

Thank you very much. Now I can create all the houses I want!!!! How do I start a new game without having to create a new sim? Or do I have o create the sim add them to a world them evict them so I can have the blank neighborhood?

You must have at least an active sim in the game to be able to edit worlds. But this is the only required step.
Once this is done, you can delete and edit any lot, also that occupied by your sim.

Sorry to be a bother how do I delete a whole lot? Or do I have to enter each lot and use the hammer tool?

Unfortunately , the only way to demolish a lot is to use the hammer tool in Build Mode.
Then, like you said, you have to load each lot. You can't do it from the screen of the world.

I think EA has a few things to work on. Thanks for your help. I found a sort of quicker way. I still have to enter each lot but instead of using the hammer tool if you click the icon that is lot info panel, there is a bull doze lot icon. I used that and the whole lot was bulldozed.

Yes, sorry.
I meant to say bulldozer button and not hammer tool :P
Bye

Thank you for help.

Sorry to be a pain but how do I get rid of this sort of double wall? I got it after I first bull dozed a lot then tried to build on it and I got rid of it. But I can't remember how. I am now on another lot and have this wall again.

If you change the lot type you can delete the entire lot. I usually choose "Generic" so I'm not sure if it works with other lot types. The game gives you a message about going into build mode. Do it. At the top there is a bar with the lot name and some other stuff. On the right side of that bar is a bulldozer. Use that to bulldoze the entire lot.

Edit: Just saw this answer given above so I'll be helpful in another way.

To remove the higher walls:
Click on any portion of your building that is enclosed, i.e. a finished room. You can just make a tiny square if you want, then bulldoze and build as you see fit after you adjust wall height. Above the move room tool (arrows) there are 3 bars. Those are wall heights. Click the left, smaller, one and you have small walls. You can do this on any floor for varying wall heights. You cannot, however, have different wall heights on the same floor.

Also: If you hit the "u" button you can select the entire building and move it if you need to.

You could also download 2 emty worlds. Check the following website, saves you al lot of time and work:
The Sims 4 empty worlds

Hope this is what your searching for.

In the first post he said he wants to keep his saved games.
These empty worlds that you've linked replace the whole worlds of all saved games
From modder page :
"First thing first I have to warn you these empty worlds will replace yours by the time you install it.
Everything in the worlds like your sims, lots, collections, etc,. will be gone. "

Thank you everyone. I figured out how to fix the wall issue I just had to adjust the height. Didn't know I could.