Here is how I've made my DIY T5 fixure.
It cost me less than $230 w/o bulbs, while original ATI Sun Power would be $550 shipped from Germany. With no guarantee, spare parts nor service (no ATI partners in Ukraine) and near-zero chances for reselling (no one needs T5 here, too pricey for Ukraine anyway).
So, frame is made of the cheapest pine plank I've found. Dimensions are 20x80mm (approx. 3/4 x 3"). Six coats of hardwood floor varnish applied. This fixture will be incorporated into canopy some day, so it doesn't have to be fancy.
Aluminium rails for acrylic splash guard installed.
Same rails are used to hold waterproof G5 sockets in place.
Six ATI 39W bulbs installed along with aluminium Dennerle Power Reflectors.
Three Vossloh Schwabe ELXc 240.863 ballasts are used.
Finally, the wiring is done.
120mm fan and a lid will be added later, if needed. But for now, I'm considering it done
Wow! Nicely done!