|As Richard pointed out, your distance exceeds the limitations of Cat 5e/6 cable by quite a bit. This leaves you two options. |
One, fibre optic cable which again, Richard already pointed out. The second is wireless.
You could buy two wireless point-to-point antennas and connect the outbuilding that way if you have a nice clear direct line of sight. You won't of course have as good bandwidth or reliability with wireless, but that's the price you pay for the convenience. You should still be able to easily get minimum 100 Mbps bandwidth with decent antennas.
I suspect you'll find the fibre optic is too expensive since you'd also require two media converters (one at each end) to convert from fibre to copper. Also, a preterminated multimode fibre optic cable isn't cheap.