Here in NWFL and much of the south humidity can take its toll on materials. Take this drywall for example. This is roughly 30 years of patch work and leaving a garage door open when it should be closed over night. Eventually the drywall will sag and mud will chip away due to moisture and temperature changes of the days and seasons. You can patch, then re patch again, but eventually it starts looking really bad. The reason for the drywall is for firewall and prevention of fire spread should something happen in the garage. I'd say double up your drywall for the wall between the garage and main house or use fire rated drywall for that and use what you want for the garage ceiling and walls. Here's an alternative for your garage ceiling. We used Corrugated metal. The cost was cheaper, the install went quicker and I think it looks better. For trim we used a roof eave trim. Personally I think this does the same job if not better for fire prevention, but there is always some inspector out there that thinks otherwise for EVERYTHING. When you buy or build your home on your property, it's yours and that's where that whole 2nd Amendment / Hell off my property Mr. Inspector or anyone that disagrees comes into play. Have Fun! :)