Help!

Ok chaps, I'd like the benefit of you experience please. Should I make my shed floor 4", 5" or 6" thick? Vote above please to cure my confusion!

Well today I made good progress with levelling the site. Although there is hardcore over most of the area, the front right corner is, for some reason, a little bit soggy and although there are loads of rocks, they're a bit far down so I scooped all the top soil off and now have a firm base upon which I can pile stones, rocks, rubble etc to bring it up to the same height as the rest. My next move was to start chopping bits of wood up for the shuttering. I'm a tad embarrassed to say that I didn't buy enough in the first place, 'cos I'm having to use two lots of 4" as they didn't have any 8 or 9" boards, and I forgot about the ones that will go across the middle (so that I can lay the slab in sections). Not ideal but needs must. Also not ideal is the fact that when I have the sandy ballast delivered, the driver will probably want to dump it at the top gate, some 50 or 60 yards from the site, as last time they delivered, their truck got stuck at the bottom of the drive. Come on, get voting, how thick should I make the floor?