Just be careful if you're hanging angled flats...make sure you get rigging rated for overhead lifting (no quick trips to home depot) especially if you are using hollywood flats, what with all the extra weight chillin' over the actor's heads.
Addressing Footer4321's comment about flex, if you have rafters or I-beams above your space, you can add lines from the attic ceiling to the rafters to reduce the flex. These would be hidden by the angled ceiling itself. If you can't use extra lines for some reason, you could mask support beams on the stage itself with old boxes, trunks, wardrobes
etc. All things that would be in an attic normally...just some ideas