A thought, and I don’t like it but I think it would solve some of the problem. Get a good sized concrete saw and cut two notches the width of a trench drain apart in the open side part of the building as close as you can get to the wall of the enclosed building. I’m talking the full length of the wall. This means you’d then have to pour a bottom to that which slopes to the back and dumps out. It might take a pipe to get it to daylight. You can put a grate over the channel once’s it’s built.
In the back would it help to cut off the concrete?
You could also cut a small square inside the building and have someone directional bore into the building and pull a pipe to the outside. I don’t know if one drain would catch it all though.
It’s a shame, nice looking building.