Sorry, but I am not a fan of any plan that includes burying copper pipe in a shallow trench. (Damp + copper = green nightmare.)
I would be much more in favor of tee-ing the pipe at the level of the tank outlet, and going UP with the the supply line to height of say 8 ft where it would exit the shed and travel to the garage. I would install a drop on the other end of of the tee inside the shed, along with a drain valve near the floor.
I don't know what your run length from the shed to garage might be, but I'd suggest that it should have a slight slope to it as water vapor is sure to condense in the outside air ... especially in winter ... and you don't want ice to form in that section.
After the air has entered the garage, you will want to install another tee, and another drop to shed any moisture. You may even want to manufacture a cooling tower like mine (see my journal) and a filter.
My plan from there includes a horizontal supply path to each "work-station", then a vertical drop and drain on every work station. Each outlet is teed with short horizontal tees for for a female coupler, with a drop and drain valve down below it.
The theory is that it should be nearly impossible for accumulated condensate (H20 liquid) to ever make it to any outlet that I attach a hose to.
Best of luck!