Having just replaced my dirt floor in the old section of my shack with concrete (last summer), and built an addition to the shack on a concrete slab, that's the solution I'd recommend. It was a ton of work, but it is fantastic. But you can go wood off of a footing/blocks/slab if that gets you high enough to solve the grade issue. Without seeing it in person, this would be a very general suggestion. If you can find/borrow some porch (screw) jacks, you can raise the building high enough to get the wok done. Run two girders of steel or big enough 2bys to support the load, and use the jacks to raise those evenly. Support the raised girders/structure with solid cribbing - not concrete blocks because they are not designed for a point load and may collapse without warning. Be safe, not sorry. If it's beyond your abilities, get someone in to do it that knows what they are doing.
I dug out the ground/rock on the high side of my shack, and will have to do some more work on the grade this year, but no drainage issues as of yet. I'd do just about anything to get off a dirt floor!
Gary / Zena Crossroads / 42˚ 00' 24" N / Hobby in Early '70s, Addiction since 2014
175+ taps on 3/16 (60 of which are on two Lunchbox Vac/Releasers)
12x34 timber framed sap house w/attached 10x34 shed roof for storage
2 x 6 Smoky Lake hybrid pan on Corsair arch with AUF/steam hood/preheater/concentric exhaust
7.0 KW Sun Power PV System, Smokey Lake Filter Press/Steam Bottler, Modified NGMP RO - 2 4x40 posts 200 gph