That’s a beautiful building, and will make a superb workshop.
We have had jobs where water has been coming in right at base level, and we usually dig out, and water proof the bricks or blocks with a bitumen like coating, or even lead flashing, then run an Aco drainage ststem all around the perimeter of the building. Then run the gutter downpipes into the drain also. This cures the problem.
It’s looking great though, I’d love that in my back garden!