I think I might start by going over the roof with the rust converter "paint" - forgetting the name right now, but rather than just covering rust and letting it keep working away, it reacts with the rust and stops the action.
That step would be a good idea, no matter where you want to go with it from there.
Depending upon where it is on your property, and whether it can be moved, the choices of how to use it could change around a great deal.
It could make a terrific little work area for potting plants and prepping seedlings, especially if it's near a place you're going to do a bunch of planting.
It could make an "outdoor" kitchen with the addition of an appliance or two.
Would be a great cabana near the swimming
pond.
Could be a guest room, with a little modification like curtains and a sleeping area.
Got a resident artist/craftperson whose medium is messy? Might make a good studio and get the mess out of the house
It could be a chicken coop, or rabbit hutch - but I would think those uses are lower on the list than those that are directly human utilization.
Again, depending upon where on your property it is, what your overall goals are and whether it can be moved - I think it would make a great Sign for a
permaculture farm market. Park it right up at the main road, paint it up to look really great, and use the interior as sheltered market space and a location for your honor box or cashier, depending on how you wanted to operate.
That's about all I've got for now