I know that polycarbonate sheets are often used for crystal caskets, and similar, but I'm curious to know how it compares to wood and aluminium as a general building material?

Of course you can work with polycarbonate, but it has a small drawback when used in bigger props.
When it becomes a dent, then it's difficult to repair. So you have to replace the piece.
Another "problem" is that the material often glares in stage light. On stage colors normally have to be dull.

Look here for several threads related to working with Lexan (polycarbonate):

http://themagiccafe.com/forums/search_re......=7466323