I used 1-1/2" thick rigid polystyrene sheets for my walls. I painted it with primer and then gloss with paint with an additive to help with lower burn rate. Building is not attached to any living spaces. I may add (glue to the foam) FRP panels in the future.
The coating on my Bend Pak runways is terrible, however, it is wearing off quickly and will be smooth. I will weld something else on at that point.
GET BRIDGE JACKS!!!!! What use is the lift (other than just storage) if you cannot lift the car off of the tires/wheels. It costs more $$ but...