Ceiling For Fishing Cabin

Came across a way to do a ceiling that seems to meet all that I am looking for. I was wondering what would be the best sheet rock to use so that sagging will not be noticed - 1/2 sag resistant, 5/8 etc). Please note that no nails/screws will be used on the sheet rock. The ceiling rafters are 16 oc. Thanks Glenn Attachment 43214 (http://www.doityourself.com/forum/attachments/walls-ceilings/43214-ceiling-fishing-cabin-7f915c8e9cca330cfeb77a9978bafbc6.jpg)