does the length matter in terms of it being to short or to long i know the basics of them but if you make  your own are there any specs you should go by ? as far as length not width ?  

Hmmm interesting question. I don't think the length of the tubing matters, but the actual tubing design. Make sure everything inside is smooth as can be and the pipe is as straight as can be. Other than that, you should be good. Maybe someone with more knowledge will chime in.  

Avoid unneccassary bends (they turbulate the air), you do want it to be as short as possible to keep velocity high, but a couple inches wont be too bad (plan out your piping). ^ you do want it to be as smooth as possible (no weld seams, joints, etc. on the inside). also you want to make sure to place the MAF sensor correctly. It really is alot of hassle to make one of your own that actually doesnt hinder performance, and if you have the money get an AEM or Ingen. But if your still set on making your own good luck.