Walls and Ceilings - Rock walls before ceiling?

I know the ceiling is supposed to get sheetrocked first. From what I understand, there are two reasons for this:
1) The sides but up against the ceiling for additional support
2) The outermost joists lose 1/2 inch of nailable space if walls go first

Now, Im thinkng of doing my walls before my ceiling. Im not ready to do ceiling - dont have my recessed lights and need to rent a drywall jack for cathedral. But its supposed to rain near me this weekedn so I want to take advantage and work inside.

So I have these questions.

As far as butting the wall against the ceiling, is it really important? I mean, most of the sheets on the ceiling dont have anything butting underneath them. They are just screwed. Is it really necessary? And if it is, can I just take a small strip of rock, and use it as a spacer. Then I can slide the ceiling in above the walls afterward?

As for not having enough to nail to, the 1.5 inch joist minus the .5 inch from the rock still leaves you with more space than you have when you butt the seams together in all other areas, right?

Also, part of the walls have an angle greater than 90 degrees where wall and ceiling meet because of the slope. In that case I would think you can do either wall or ceiling first, right?

If you're going to hang the walls first, I would use a piece as a spacer so you could put the ceiling rock above the wall rock when you get to it. Keep in mind that a general rule is 1/2" rock on the walls and 5/8" on the ceiling.

1) I still dont see why the ceiling needs to go abobve teh walls. I mean, of course proper building techniques would have the top resting on a side.

But look at the other three sides of that piece of rock - and all four sides of any pieces that arent near a wall. They are held up by just screws. So I dont get it. Can anyone explain why this isimportant. Are there other factorrs as to why the ceiling should go above the wall?

2)Whats the advatnage to 5/8 on a ceiling? My plans call for 1/2 , of courseI could go higher - but what is the advantage specific to a ceiling?

Make sure you screw off completely and properly. Another big reason to do the ceiling first is you will get rid of a gap. Your room isn't square. if you hang your walls first you will have a gap at one end when you hang your ceiling. Be sure to pre fill this gap with mud(all purpose or quick set is best) before you tape. Go with the 1/2". 5/8" is not needed.

But look at the other three sides of that piece of rock - and all four sides of any pieces that arent near a wall. They are held up by just screws. So I dont get it. Can anyone explain why this isimportant. Are there other factorrs as to why the ceiling should go above the wall?

I do it because I was taught to. I can guess as to why, It may be because the intersection at the walls and ceiling is subject to more movement and is more likely to break free, when the drywall on the wall is butted to the drywall on the ceiling it offers more support and is less likely to break loose.

Whats the advatnage to 5/8 on a ceiling? My plans call for 1/2 , of courseI could go higher - but what is the advantage specific to a ceiling?
1/2 inch is fine for a ceiling on 16 center framing. If 24 I personally would hang 5/8 as it minimizes any possible sagging between the joists that can and does happen over time.

Coops,

Ive been told to screw off many times. But never to screw off "completely and properly"

All kidding aside... what do you mean by "screw off completely and properly"?

Should be screwed off 12 inches on center in the field, 8 inches on center on the border( basically 5 screws per stud except on the butt ends where there are 7). Also make sure not to sink them too deep, just below the surface of the paper, without actually tearing through the paper. Screws that are too deep don't hold as well.