If you mean the top panel, then it's made of SMC (Sheet Molded Composite.) For structural bonding, GM recommends the following adhesives:
GM Goodwrench Plastic Structural Adhesive (P/N 89020330)
Fusor 127 EZ Structural Adhesive (GM P/N 12345726)
These aren't DIY repairs unless you have the proper training and experience.
CC