Autocockers are no more of a challenge than Phantoms I would say, and I have built both.
Just start hunting the bst for parts you want and then assemble it. You can do it on a budget if youre patient and you accept that you wont have the top of the line parts, or you can spend alot of money. I spent alot of money and am happy with my finished product; I dont ever need another pump.
Then you just have to tune it, which is probably the more challenging part.
If you have any questions Id be happy to help. Good luck!