Wood floor for a workshop

Im would like to build a wooden floor(suspended) for my new workshop, the area is 7x12m(shed is 24x12x3.6m)

http://img.photobucket.com/albums/v725/ST170ish/1-2.jpg
http://img.photobucket.com/albums/v725/ST170ish/2-2.jpg

The idea, all in cca pine 200x50 bearers at 1400 centres with stumps 150mm rounds at 1500 centres, on top of this 150x50 joists at 400 centres. the floor itself will be 22mm red tongue(treated).

The shed needs some edging to weather seal it, I was thinking of re-excuvating the fill I put in(450mm) and digging down an extra 200mm to give a height of 750mm(20mm higher than the tin,tin is 100mm off the fill)of concrete wall, this wall will support the bearers at the ends and support the joist's on the long sides. The RT flooring will be supported all the way around.
The concrete wall will need to join into the shed footings, was thinking of doing a section at a time between the footings, chemi-setting reo into them.
At one end I need an opening to have acess from outside, as I want to have my dust extraction pipes and power for machines under the floor. Plus it will allow for some ventilation.... and storage of turning blanks:cool:
I'll be concreting in the stumps 300mm in ground.

Can you see any problems?
Do the spans seem ok(remembering its a woodwork shop, my heaviest machine is about 250kgs)

I've included a sketchup file for a 3D render... its only roughed out so far.

Attached Files http://www.renovateforum.com/images/attach/skp.gif floor3.skp (100.1 KB)


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