detached garage - flat felted roof - ceiling inside.

[Manchester6653u]

Hi,
I have a detached garage with a flat felt roof. I've recently painted the floor and walls inside with garage paint and I now want to make the ceiling a little more comfortable before I set up my multi-gym in there. Can I simply nail some sort of plywood to the inside to construct timber to make a clean ceiling? or would I be best doing something else first ?

Also, is there a special timber paint I can apply, its all dark brown at the moment, which I'm guessing is the stuff they've used to treat the wood beforehand? That and cobwebs.
any advice appreciated.

thanks

 

[Xenon]

Use a white laminated hardboard, well fixed for a reasonable finish. White polytop nails will improve looks.