Well, it’s unfortunate, and it will be expensive to replace, but my thoughts are:
As long as we’re doing it, cover the entire concrete slab area, kitchen area included. Maybe pour the missing southeast corner as well. The missing northeast corner is steep enough that leaving it as grass is probably okay.
Bring the eaves of the structure down to possibly 8 feet from 10. Having some slope on the roof will make it drain. The flat roof dripped for a long time after a rain. Lower eaves will give shade earlier in the day.
Build it with welded steel trusses. Possibly concrete or masonry columns. I suspect part of the issue here was rot at the base of the wooden posts. I’ll have to get out there and look. One turning loose would be all it took.
extend the roof on the west side, and have a vertical plywood wall on the edge of the slope. Put in some hammocks or shelves to hold PGs and harnesses out of the wind and sun. That will leave more space for people on the east, social side of the container. It will also cover up the ugly infrastructure side of the container, and shade the A/C unit.