Hehehe, have fun custom building your gun, I did.
Took a good 5-6 or so months, and is still not all the way done.
The only problem is fitment in some areas, IE this brand does not fit 100% with this other brand or so. And usually price, having to source this part and that part all differently tends to rack up a higher price then buying the gun pre-built by some company.
It's a great feeling once it's all done, or close to it.