In Digital Pro, you will go to the top menu and find EFFECTS/SKEW OBJECT

You will grab the top size dot and drag it to the right, to make the rectangle skew.

Now, make a duplicate of your roof piece for the other side of the roof.

You will need to flip the duplicate.

Once you have it flipped, you will need to go to your righthand stack, and grap the flipped piece and drag it down to the bottom, so it sets behind all the other pieces of the house. Once there, you can arrange it behind, so it looks nice. I shaded mine just a little. You can do this by going to TOUCHUP/BRIGHTNESS & CONTRAST and sliding the brightness bar to the left, to make it darker.