I want a a large Go-throughable object layer,kinda like BB's safe base roofs.

Why? I'm not telling unless I have too.

For those who need more of an explaination of what I'm talking about:

It's an object,A huge flat square parrellel to the ground,I want to be able to go through it.

Uh...I know that in your mission file you change

Scale: 1 1 1

To

Scale: 0 0 0

And that lets you go through it and I guess that answers one Q for yas but, I don't think TT has that shape of object in it, so youll have to import, I can;t help yas there sry :[

Thanks!

All I need now is a flat square...

You could make that really easily on Milkshape...just make a square. :)