I have made panels in the ceiling below as well, if there are no other options. It really depends on what you are making the deck out of, ie: will the sides of it be finished in wood, drywall, tile or what? One general way to do it is to start with a 1/2" piece of plywood, or the same thickness as the surrounding substrate, and keep a 1/8" gap all around. Then use self adhesive velcro strips to hold it in place, then finish the same as surrounding and maybe calk the 1/8" gap (with silicone, not adhesive calk). Then when you need access you cut calk with razor knife and stick a piece of very stiff wire, or a nail, into crack with a bend in the end to grab panel and pull it out.