no, but anymore than 2 or 3 boards on a roof rack is pushin it... i dont like using a roof rack for anything other than ladders or lengths of timber... sheet material on a roof at speed can be hairy...
nothin to stop you gettin boards delivered..
any amount of boards and you would anyway...
its just that to overboard a ceiling you need anything from 4 to 10 boards, and personally i wouldnt wanna be shoving em on the roof, and its a small amount to justify a delivery cost, but if you can make it pay any other way, just get em delivered with the plaster, pva, scrim etc, order over the phone and have a lie in ;D
coving, up to 2/3 packs is usually ok on a roof, well secured...
but what if its p'ssing down....