Beautiful tractor shed - love it.
FWIW I am on a ridge and have gotten
many tough lessons from mother nature on water flowing downhill - H Sandy & H Isaias in particular.
I had an existing detached garage and added a 12x38 tractor shed close by perpendicular to the fall-line slope (fwiw designed for & dimensions ideal for my OLD property i.e. I brought it with me).
The above advice is right on from
@Mountainhill in that you need to grade above & build-up / add gravel on the access lane.
I am able to get by w/o a culvert and ditch but added one under the middle of the shed due to long narrow size and grading essentially created a basin (I was not able to build the base up as much and slope is higher than yours)