If you have a chop saw, or band saw, and grinder, along with basic hand tools its as easy as marking where the cuts need to be, fitting, thinking, maybe some measurements and then cutting.. Then of course, welding them together. You really have to put some thought into the design and layout though.. Don't want to fab up a whole kit and have it not fit, or fit poorly.
To make it nice, and look really nice takes some skill, but almost anyone can cut and weld, and make a turbo setup that will make power. And im taking a guess by saying you must be mechanically inclinded somewhat.. Otherwise you'll get aggrivated and give up on it, like some do.