Quick disclaimer - This project could cost differently depending on where you are. Substitutions can definitely be made. Equipment - Drill, Drill bit, Phillips driver, Wire strippers, and a saw. This guide is for US residents, your plugs and voltages may be different if not residing in the US. Lastly, electricity is pretty dangerous so stay vigilant. Always consult somebody educated with electricity before using it.
The fixture was made of birch, but any wood is OK. Two holders were made to cradle the side of the tank so the fixture would not fall off if jostled. Another two boards, just tall enough to fit the lights underneath, were installed to support the fixture from the side of the tank. The largest piece, where the lamps were mounted, was (1/4" + 2*Wood thickness + Tank length). The side cradlers were 6" but any size works. Supports were (lamp height + 1/2") to ensure that they could hold when the lamps were mounted.
Lid was ordered through TAP plastics. You can cut polyacrylamide but it's just so much cheaper and more worth it to order online. Plus, they machine to 0.001cm so they're very precise with your measurements. This tank will be a LL tank so it will have stagnant air, and a small fan will circulate once or twice a day.
A plug was attached to the cord, by stripping the wire and screwing in the wire around the screws very tightly. An outdoor rated plug, IMO is the best thing to buy for plant stuff. Follow the manufacturer's instructions because every plug is different. If you get the option to poke a wire through a hole, and to screw it in, always choose the screwed connection. I didn't want a plug with a ground. You can choose one, I recommend grounded plugs in most cases except, as mentioned below, when you have AFCI breakers (which do not require a ground) and have a timer without grounding, it is OK to consider a two-pronger. Check your fuse-boxes and circuit breakers before choosing parts.
You can use wire caps to connect the wire to the power supply of the lamp. If your lamp uses a transformer, attach the wire to the high voltage side of the transformer. Remember - Black is hot, White is neutral. I removed the green wire since I do not have a plug with a ground. If you have a plug with a ground, connect green to green. Fasten tightly and securely, to ensure a good connection.
Time to attach the lights! I drilled some tap holes and screwed them in one by one. This is difficult especially since the mounts of the lamp are hard to reach. Two screws, diagonal, were used for this, in case of error, to make removal easier.
The lights were attached to the power supply once all of them were drilled in and it lit up! Always check before doing the final steps. I finished completely screwing each of the mounts in. Be vigilant of shorts when plugging in, remove the plug if it 'sparks' in the outlet.
Final view - Awesome, and it looks pretty. I hope I have disproven the common belief on this forum that DIY setups are ugly. This one is awesome, it's stained hardwood and a nice tank.