I also vote to build one. You can make it the way you want it. When i started to looked at the off the shelf AR9s, I did not like half the parts in them,
You will learn a lot, what works and does not. Keep it simple, stay with the same company manufacturer for parts as what "texasdawg" mentioned. Years ago New Frontier Armory sells an AR9 parts kit, you can change parts. They can assemble for you but that spoils the fun part. This also gives you kind of a tech support for parts that will work.
Like you said its not your main division. Why not expand your experience in building one also?