I need to make a cake of a building and I need to make air conditioner units and other objects to put on top. I am trying to make a rectangle shape for the air conditioner out of Wilton gumpaste. I keep getting cracks and lines in the gumpaste. How can I get it smooth and line free? Thanks for any help you can give me.

I put a bit of shortening in my palms and then gently roll and roll and roll into a ball until every single crack and line are gone before I start shaping. Then you can gently shape it into a rectangle. HTH

I have tried doing that but maybe I was rolling it too hard. I will try to be more gentle. Thanks for the suggestion.