Check the below blog..
http://holynerdvana.blogspot.in/2013/11/litecoin-mining-with-r9-290-and-r9-290x.html
The blog has a decent build guide for R9 290's but just remember... the most important aspect of mining aint the GPU's its your PSU... so dont cheap out on it
https://bitcointalk.org/index.php?topic=7216.4240
chk post number 4255 and 4257
Note that comment- has hard time running 3 on 1000w without it crash
thanks a lot I searched some experiences and you gave me it