I am building an underground storage facility. Size is 20' x 40'. I
need to know size and quantity of steel support beams and corrugated
steel specifications for a concrete roof.

Loads (psf) are as follows:
Snow = 25
Soil =  240
Transient point load (bobcat spreading soil) = 125
Live load = 40
Soil (can be considered dead load)  = 240
Dead load of concrete cover (4 inch thick at 4000 lb's per cubic yard)
= 50 (weight of beams and corrugated steel need to be added to this)

I would like to keep beam thickness no more than 12 inches or so.
Beams would run the 20' length, single span, If necessary, to keep
costs and beam thickness down, support columns can be added but would
prefer a single span.
The foundation will consist of concrete footings and 10" concrete walls

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Request for Question Clarification by redhoss-ga on 04 Aug 2006 06:52 PDT

I think that I can help you with your question, but we need to clear
up a few things. Have you selected a corrugated steel panel. We need
to know the exact panel you plan to use and find a span table for it.
I don't know how to handle the weight of the Bobcat. Depending on the
weight of the model you will use, I see ground pressures listed around
3 to 4 psi. This would translate to 3.5 x 144 = 504 psf. If you took
the weight as a point load the weight could be around 5,000#. You
could put temporary bracing under the beams while spreading dirt and
ignore the Bobcat load. Your other loads look like reasonable numbers.

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Clarification of Question by weeping-ga on 04 Aug 2006 18:30 PDT

Please remove the bobcat load from the equation. 

Can you calculate which decking to use based on the loads indicated?
Span charts for steel decking are avaiIable on the website of United Steel Deck.

Also, please add a safety factor of 25% when you have determined beam sizes.