Barn conversion first floor construction???

[bigtone]

Hi all,

I'm about to embark on a barn conversion in the south of France (next year) and I was hoping someone might have had some experience in doing so. The barn has 500mm thick walls and has enough height for 2 stories. It is currently open plan and I'm wondering how to create the first floor. The barn is 15m long x 10m wide. I was thinking of using oak uprights at mid span of 5m (of the 10m width) and using large oak beams to span the 10m (maybe 2 x 5m resting midspan on the upright. I would then come off these with the joists. I suppose I could go down the RSJ route but as its a barn, I'd like to use some uncovered oak. Anyway, I'm not sure what size RSJ I would need to span 10m in one go. Was thinking of 1m cubes of concrete for the uprights with some thick threaded rod protruding so the uprights can be slotted on top.

Any thoughts?

Cheers guys (and gals if there are any)

[welsh brickie]

Cut the stone out and insert padstones made of reininforced concrete,then lay your steel beams ontop.
A central pillar is needed because of the span,this can be oak but the steel, can be clad in oak to disguise it.you may need to cover the steel in fireproof plasterboard,for building regs