[Stiglr]

To further your non-perfect roof example...

to make it less-than-symetrical, after you've described the basic contour, subdivide it, then grab groups of vertices along the lines leadiing to the center of the roof, and move them up and down to create the effect you want. You can go anywhere from using say four lines on the same Y axis height and move them all together... to creating a falling-apart roof with very random areas where the surface may have sunk in from rain damage or tree strikes.

Or, you can let the computer randomize the contour with the Noise command.

I suggest, as I usually do, getting a copy of the User Guide from the Downloads page of this site and look through it. Not only do you learn more about the various commands, you get ideas about how you might use them, and guidance on how to create types of models you might not be familiar with.