Going back to the original question for just a moment, none of the castles I've visited in England had wooden floors in the outer defence area. They're all thundering great slabs of stone, supported as Larb described by vaulted ceilings below. What you've got to remember, however, is that back in the day the average height for a man was only 5'4" due to the harder less well-nourished lives people used to live back then. Nowadays most women would be taller than that, and in fact some of the crenulations on the Welsh castles are too dangerous to allow visitors to go up the smaller towers without a guide, purely because they only just come up to the belly on us taller 'moderns'.

So the vaulted ceilings were nothing spectacular in the outer defence work - the walls and the towers, because the stairs were really quite small, and so were the rooms (except in the inner parts, like the keep).

Wooden floors would have been something of a health hazard if you think about it, since I imagine the first reaction to discovering your men were dying just trying to get into the towers would be to set a bonfire at the base of the stairs and smoke the defenders out. It would work even better, of course, if the floors were wooden.

Maybe a bonfire would be impractical to build if missiles rained down from above whenever the tower was approached, or it would have been done again and again... unless... maybe the medieval armies were not so inclined to such horribly evil ideas! I'm really not so sure I'd be able to do it if I was transported back in time and put in charge of a failing invasion force. I think I would be more inclined on second thoughts to starve them out instead. I mean - just how much food and water can you keep in a tower that's stuffed full of men and munitions?