u can do that all with paint and some latex. use the latex to build up sections on the wall like mold and mildew and use paint to do the colors. put a nice splatter of paint on the wall and use a spray bottle and mist the paint, this will cause the paint to run and gve you nice natural streaking down the wall. pretty simple effect. same goes with the ceiling. lay a basecoat color down then cover the ceiling in latex, paint the latex the color you want your actual ceiling color to be. after everything dries take a knife and put some slashes in the latex and peel it back exposing the lower layer. wala.
Without doing major damage or plaster work to achieve this, would go for another option.
Attach sheets of clear plastic to the ceiling or overhead. This will achieve a look of it either being closed off because of safety or look like asbestis removal. If you hang them staggered from left to right it will block the clear view of patrons. Fallen warning tape would be a good touch also. Hang a large flourscent light fixture at an angle from the ceiling to give the illusion of it about to fall. Loose conduit hanging around from ceiling to floor. Shredded cheese cloth hanging from the ceiling will look like the ceiling is starting to come down. Dimly light the area to make it more creepy. Empty wheel chairs (at least one of them laying on it's side) would also help the look of it. Don't forget the gurney with either a faux body or actor, covered by a sheet.
