I can see both sides:

1. Love the pride in doing something myself
2. Having things done right

Most of the time, unless you have the skills and the expensive tools, the two do not go hand in hand. Personally, when it comes to turbos, I'd rather have it done right by having one fabricated specifically for my car. It is sometimes cheaper, and it is a guaranteed fit.

I always look at turbo/supercharger kits as a generic kit. Basically they give you pieces that should fit your car, and sometimes you end up having to get stuff fabricated anyways (adding cost). In my opinion it is easier/cheaper to have someone start from scratch rather than modifying something which is already fabricated. Because a one-off kit is custom fabricated for YOUR car, little things like pounding out a portion of the firewall or "modifying" the k-member can be avoided just by routing things a bit differently.