Good morning!
I built my deck with two doubled 2x10 beams, (beams were set on outside edge for where tub was going to set), and attached to the house with thru bolts, I used two 2x10 for joist on 12 inch centers, then used two sheets of 3/4 ply under tub. All lumber is pressured treated. The rest of the decking is 4' x 4' squares of 2x4 and 5/4 decking. I make up these squares then set on joist like flooring!good luck
john