after spending the money on joints, DOM, bushings, plate, welding wire, gas, nuts/bolts. its going to add up to be about the same maybe save 200 bucks. time is money and the time you spend learning the geometry, mocking up parts, you be so fustrated that you didnt save up to buy one. thats just my opinion.
now if you have all the material laying around and know what your doing, it could be done pretty quick. leave building those to the pros,