I have all sand so i plan to put a third beam down the center. I am planing to extend it to 32 or 34 feet also. There will be 5 piers poured in sono.tubes sitting on a 2' x 2' x 10" pad.  The tables tell me sand is good for 3000 lb per square foot that totals 60,000 lbs.

Is that enough for the 20x30 even if i extend it? Im doing the work myself so slab is pretty much out of the question. I was thinking of a 32' x 16" footing for each beam if i have to but even that much would be difficult.

You should check the loading and bearing capacity out locally, but I did a quick load trace using 30 psf for your snow load. The center bearing beam under the main floor carries 1/2 the weight of the two outside beams. Tracing down the loads I come up with 1,000 plf on the outside beams and 500 on the interior. If your pier spacing on the outside beam is 7' o/c (say 35' long w/ 5 spans) then you will have 7,000 lbs of bearing at the full span piers. Going to a 60 psf snow load adds 300 plf to the outside beam, or 9,100 lbs at the pier. Recheck the foundation beams and bracing for this design. The glulam will likely be better than the built-up beam. Pier bracing is more important in sand as it has less lateral support.

You might look at the Bigfoot system as you can do one pour and the footings may be large enough for your needs. http://www.bigfootsystems.com/

Forgot to mention. Southeast tx. We dont do snow. Never gets below freezing for.more then a few hours.

I was looking at the bigfoot system already.

I.was thinking 8 foot between. Piers but i could change that.

Was planing triple 2x10 pt beams 2x10 joist between them on hangers. Mainly because 10 &12 foot lumber is.much easier for.me to transport then 20 foot. I know.i can use 2x8 joists but its just $0.30 more per ten foot board.

I was also planing on a center post floor to roof in the middle directly over a pier. And a beam under the loft floor from end wall to that center post.

Do the plans come with elevation drawings?

We have no.building codes here except im building in a lake community so they do have to approve of the foundation before i can continue. In order to get the permit they want an elevation view of the structure

Yes the plans have four elevations. Also three foundation system plans - for pier and beam, slab and concrete perimeter crawlspace.