Walls and Ceilings - What drywall thickness?

I'm rocking a barrel ceiling that has a 48" radius. Should I use 2 layers of 1/4" or 3/8" or try to pre-bend 1/2" to fit. The framing are flat 2x4s 3 1/2" apart and the ceiling is 16 ft long. I was planning on using 4 sheets hung across the arch. If I were to prebend 1/2", what is the best technique? Also I would appreciate any suggestions on sheet rocking over cracked plaster, both ceiling and walls. Would 1/2" on the ceiling suffice with adhesive and screws thru the plaster and into the studs? Thanks for your input.

for the radius I would use 2 layers of 1/4". 1/2" would be a major pain in the neck to bend. It would break more.

For laminating over plaster, 1/2" is best. Definitley use glue and screws like you said you were. Good luck.

Thanks for the advice. Do you think the 1/4" will "segment" or flatten on each 2x4 as it is attached or will it arc smoothly? Are there any handling precautions to prevent breakage (I've never used 1/4" sheetrock). Also do you recommend using adhesive or anything else between the 1/4" layers. Thanks again.

It's going to be a challange for sure. Ive broken 1/4" picking it up. Some spots will be great and others will flaten out and break. The quality of the finishing is what is important. A good finisher will make that look great.

I wouldn't use glue. You are going to have to screw it off a lot to get the look you want.