The router that I am building OpenWRT for is TL-WDR3500 TL-WDR3600. I will be building Attitude Adjustment, Backfire branch
BASE BUILD
(1) Set up build environment
$ sudo apt-get install subversion build-essential libncurses5-dev zlib1g-dev gawk flex quilt git-core
$ mkdir ~/OpenWRT
$ cd OpenWRT
$ svn co svn://svn.openwrt.org/openwrt/branches/attitude_adjustment
$ cd attitude_adjustment
(2) Configuring the build
$ make menuconfig
Fill in target system and target profile
Select Base System, check install is minimal and save
(3) Compiling
$ make make -j
(4) Installing Image (assuming the above is essential)
Fireware images should be located in /bin, the correct image for flashing over the original firmware end with factory.bin