I am considering welding a small tower/platform (about 5' tall) for a 1500 gal. poly water tank. The tank is around 8' in diameter and around 5' tall. The tank full of water should weigh somewhere around 12500 lbs. I would like to build a majority of the frame out oilfield pipe maybe 2 7/8" or larger if need be. The posts could be 2 7/8" on a 4' with girder like cross pieces made of i-beams with purlins placed on top of the i-beam spaced maybe 12' O.C. and sucker rod x-type bracing. How many posts would y'all recommend and what are your thoughts on the the rest of the design and what sizes would you recommend for the i-beams and the purlins?