Problem with Diy is warranty there is known one fuck up and you threw your money away like i said depending on what the grower wants or has for room LED might be a good choice i am not defending Hid lighting i use what works for me and my situation
there are many advancements in grow lights one being CMH this is another possible way of going instead of led lighting
its what works best for your situation
As for Chip on board ( cob ) i believe there are heat issues also the angle 120 degree which also suffers in par on outside of grow area here a 4 x 4 scrog to achieve 6 oz that is terrible not sure how many plants he ran lol but non of the less terrible
https://www.youtube.com/watch?t=114&v=r65mzeu03Po
then lets look at a 400 watt HPS grow 1 plant enough said
Again as for me having 2 Flower rooms 6 k 3 in each i achieve 15.5 pounds every 84 days 7.75 pounds per room 12 plants per room 3 k not including 3/4 pound of hash from trimmings per room this is being effcient