Typically, a crack where the top of the wall meets the ceiling is due to truss uplift. The Truss is the wood framing member that forms the “triangle” shape of the roof line. They are connected to the house using metal plates. Wood will shrink and move a lot, however, drywall will not move. Builders generally use a truss clip that allows for the roof to move up and down and help avoid extreme cracking provided the drywall was fastened correctly. Cracks of this nature are typically able to be repaired in the summer months when the lifting has lowered.