4 x 12' sheet of 14g.(12 g if used for vacuum) stainless through a standard roller. Lap weld seam 1/2" inside and out. Top and bottom 45"diameter disc with a 1/2" hole in the center and a radial cut to the edge. Using a tire rim and a hydraulic press cone up each disc 2", lapping at the radial cut. Secure and weld the lap seams. Coned top and bottom assure more rigidity and allow a better drain function if needed. Discarded corners from cutting discs can be used to fabricate legs.
I could do it before lunch in Murray KY...I'm sure it could be done faster and prettier in California.
Above tank would hold 320+ gallons and need no interior baffling if secured upright. 44" diameter x 52" tall.