I found the ideal alternative for me to be 3/4 inch stone under a car port at the entrance to a garage. I find I do more of my work that does not require jacking up the car on the stone (oil spills raked over) and other work inside. A great combi for the weekenc Mech. esp. if you need to idle your car during service and it’s a rainy weekend. Carport with rock base on a garage with concrete. More options. Post and beam consruction would allow a easy integration of the two. Besides, outdoor barbeques are still an option with the mrs., an additional selling point.
I do not think having a portable treated wood floor garage is a bad idea. I feel it has many positive points to consider rather than he standard cement floors, gravel, blacktop, etc. One huge advantage is taking portable garage with you when you move, less tax on property and using RP5217 annotating the new owners and the removal of portable out buildings, sheds, garages, etc. yes the Code does say non combustible surface and the key word here is surface. Underflooring can with todays new wood materials last as long as cement and maybe longer depending on the air cirulation and position of this portable garage on skids, it can also be moved on your property, you can upgrade it with newer materials being made, etc. etc. I am in the process with the Department of State of New York senior engineer in the division of Building and Codes to gather information for the use of aluminum garage tiles trowled on 3/4" treated plywood or the use of fire retardant 3/4" treated plywood using the self adhesive or trowel spread adhesive mortar mix laying a 14x28 portable garage at a cost of 6000 dollars for the garage and 2500 dollars for the flooring. The impact to property taxes will be very minimal much less than a permanent structure with cememt floor and taxes will do nothing but increase on a permanent structure.