I'm setting a hot tub into my existing deck. A concrete slab is conveniently located exactly where I'll be setting the hot tub, unfortunately it is about 32" lower than I need it to be. I've been told by the hot tub vendor that I need to support 222 pounds per square foot. The hot tub is round, 5' in diameter. I'd like to build a 5' square deck on top of the slab to support the hot tub at the height I need, but I'm having trouble finding beam span and joist span tables for that psf. Does anyone know what size lumber I'll need, how many posts, and the beam and joist spans and spacing? I'll be using pressure treated doug fir.

Alternatively, I have access to 9" square railroad ties. (I like this option because it's free.) I'm considering using two layers of three ties each, laid on their sides, one layer perpendicular to the other. On top, I'd use 3x8 if possible, (or 2x8 if that's what I can find,) set on edge at no greater than 9.5" oc spacing. I feel this would be adequate, if not over-engineered for the load, but I really have no way of knowing for sure.

Thanks for any advice you can give!