Rapid LED sell premade rails to put the heat sinks in.If you dont wanna go that route and make it yourself you can buy angled aluminum from lowes or Home depot or anywhere that sells it.The whole purpose of the DIY cob builds is to fit the footprint you wanna cover.
When i set mine up i took the square footage of the area 4x5 (20) square feet.I used this selection tool to select the wattage per cob and what drivers i needed.
http://ledgardener.com/cob-led-driver-selection-tool/
The goal is more cobs at less wattage for alot of light overlap.cobs are 120 degree beams so the more you have at lower wattages the more efficient.I dont really see the need to air cool LEDs honestly.for a 16 square feet you could go with 3 rows of 4 and put 6 35 - 38 volt cobs on an HLG 320 and drive them at 1400mA.
The vero D is 38.7 V X 1.4 amps giving you right at 650.16 cobs for a 4x4.Thats right around 40 watts per square foot. which is perfect IMO.
If you wanted to spend less money on the build you could get 8 of the same cobs and drive them at 2100mA with the same 320H drivers and only have to use 8.Less money on cobs and heatsinks but less coverage and less efficient.
Its worth the money to get more cobs and drive them softer.The amps you drive them at determines how many watts they are pushing.I could hook up 2100mA drivers to the cobs i already have and put 2500 watts over the 4x10 if i wanted to just by switching the drivers.