I wanted to create some nice roofs. But when I try to make roofs it keeps complaining about teh base being uneven.
But my lot is as flat as a pancake.

I could use autoroof, but I want to make some special things like a terrace on top of the house and stuff.

What is causing the base being uneven?

I noticed that happening a lot to me...I didn't spend too long doing a semi-scientific study of it (like I did with making basements work), but I think that for whatever reason, the roofs don't like being certain dimensions. Odd ones, perhaps? (Dimensions being the grid width/length of them, of course.)

I came across that while trying to make a building with a bunch of roof-covered porches, and the game whined like crazy to the point that I gave up on it, and built something else.

Oh, well I'm already having trouble creating simple square roofs for my house. :P
For example my garage, room for 2 cars. Does not seem that big.

While autoroof can apply the square roof no problem. XD
But can't have the terrace that way. xd

Turn constrainfloorelevation false, level the floor you want to set your roof up... Done...