Ply Floor down after walls and roof or before?

Just have to double up the surround on the shed base and dwang? It for attaching the ply floor. Watched load of videos on shed builds and some of the large builds the chaps leave the flooring to the last.

I.e build the frame, joists, walls and roof....then get the electrics etc done and the floor last. Would make it easier to replace in he future if need be, better resistance to damp if I dampproof between base frame and walls, rather than entire floor sheeted with polythene just in case the floor sweats?

Would appreciate any input, pros, cons etc.

Thanks....it's raining again here BTW...

 

Floor is going down last. Decision made.