Its not too difficult for a body shop to do, headliner etc all needs to come out, front and rear windscreens need to be out, plastic trims either side need to be off, you can then start to see the edge, using a small cutter etc work your way around the edge.
New roof is bonded (similar to a windscreen), held inplace with clamps whilst is sets.
sk8fe had some pics on his build thread..
clicky