pretty cool. I considered building one of these awhile back, but I had no spare cases, and I didn't want to shell out the funds for used server towers, so I never did. But I like your design and just seeing it I can tell where I could also make some small improvements.
The fan might be dragging hot air from the lamps right past the plant before exhausting it. You look a little cramped for space, but you may be able to improve upon this design some if you also had a narrow drop ceiling and had the fan directly above the lights pulling all the hot air thats rising to the top.
Maybe my idea would not work as well as having two fans in the same horizontal area, one pushing to the other, as it is now, but its a suggestion. maybe for others who might attempt the build, maybe just for me. lol
Anyways, not trying to slag on your setup or look for faults. Looks nice for what you want. I wish you much luck with your grow and further development. Thanks for taking the time to share and for the clear photos. I'm sure others will incorporate some in their own setups.