When I used a tile for building I kept a roll of white butcher's wrap paper handy and would place a piece of this paper directly over the 2' X 4" ceiling tile, then place my plan over that, then place a sheet of wax paper over that. When I removed the plan and wanted to work on the ceiling tile the white butchers paper was there for protection and I could also draw datum lines or whatever on the paper for building/assembly reference. I bought the butcher's wrap paper at a local meat store where the owner would order a roll for me and sell it at his cost; you may want to check out this option.

Soft landings.

Joe