@bamani71 You need to pull that part of the roof out as far as possible and then add a very slight curve on the roof as a whole.
https://78.media.tumblr.com/dccd39c790ed393ea7d4550d57ef647b/tumblr_p2rkzkaKSN1v8k7elo1_1280.png
This roof is actually 3x3 - I've pulled out the lower side as far as possible. You need to use arrow circled in red, but you need to hold down shift will dragging it, because it will otherwise extend the other side of the roof too and you don't want that. Then used the ball shaped thing in the middle of the roof (circled in yellow) to slightly curve the roof so the lowest part will go slightly into the ground. Also choose a small roof trim so it won't protrude through the ground.
I hope this helps :)
