That's quite the job and I feel your pain. Oh and I have one of those godawfuls. Can't believe I haven't thrown it away yet. Figured I might need to paint some dirt one day and that's about all it's good for.maintenance time
Welp I finally bit the bullet and took on my sagging foundation. The building I am using was a kit from Lowes which 18 year old me built to exactly what the instructions said. the major flaw in the design is it didnt come with sill plates (I made sure the new half has them.) This caused water to seep in where the siding meets the floor and rotted everything out but the studs and siding. Eventually I got tired of machinery falling through the floor. After several good Seattle storms I think i finally got the leaks stopped because I didn't find any dampness in the trouble areas.
It was every bit the pain in the ### I expected it to be. I started this in august and finished about 2 weeks ago. I could have gotten it done sooner but since I work full time now I wasn't too motivated to do back breaking work once I clocked off (I done got lazy.) I had to saw out the rotting OSB floor and yank out most of the original joists so I could put in new joists and cross braces. Once that was done I had to lift one corner of the building up about 2 inches to get it "level enough." Now it has joists running every 12 inches with cross graces running every 24 inches. The new floor is pressure treated plywood that I coated with mis-tinted exterior paint. The new floor is also set up so most of it can be removed to access the joists and pier blocks if it sags again. the only parts I can't remove are where the walls are. Once that was all done I put in sill plates and sealed every possible gap with 9000 cans of expanding foam.
This probably cost around $800 for all the repairs and the loss of one godawful wagner paint sprayer
Props to a buddy of mine for lending me the jaws of life to get this done
anyways here's some pictures of my miserable month