IMO, DIY (LED) projects get rather complicated rather quickly, with a steep learning curve. And, in the end, it still works and looks like DIY.
If the subject matter holds your interest then more power to you. If you want to get to the point of plants growing and fish swimming then buy off the shelf.
I agree if the hobbyist isn't very diy oriented I would stay away from making a fixture. Not to mention with the voltages we are talking about when wiring a fixture, it could be very dangerous if care isn't taken when working on it.
However I will say now that I've been around the block with making my own fixture using 3w led stars, LDD drivers, and a TC420 controller I don't think I'll ever use a consumer light fixture on future tanks.
Once you know what is going on it's very easy to mix your own led's to suit any color spectrum you want.
Also once you get over the hump of acquiring the hardware to assemble and make the fixtures things get fairly cheap compared to AI, Kessil, Ecotech fixtures.