I have made 2 or three different ring flashes over the last two years, and have finally found one that I think makes the grade. With that being said there are a few things to mention.
POWER - DIY ring flashes that incorporate speedlights will not have the power of a commercially made one.
AESTHETICS - It probably will not look as cool either.
USEABILITY - Not being tethered to a wall or larger power source will give you freedom to grab and go anywhere!
"THE LOOK" - You still get that same great head on light with the full subject shadow like the commercial ring flashes.
$$$ - And this one is huge compared to some of the more affordable models ($399), you will only be spending around $ 20-30.
I could explain how to make this but the videos explain it so much better.
I did two things differently. I used flat stock aluminum instead of galvanized steel. I thought it might be easier to work with. The bends on the flatstock were different due to the fact that I do not use the hot shoe sync cord he uses, instead I use STE-2 or radio triggers.
Below is his 2 part video tutorial.