Alright some pointers on making yours, and actually I have one over my 20 gallon long tank. The length I cut my raingutter to was about 30 inches to 30.25 inches, long enough so when you add the end pieces they sit on the plastic rail that goes around the top of the tank.
First the holes in the rain gutter, all these need to be felt out according to the hardware you get, a nice set of drills in all sizes comes in handy here (or a dremel). Cut small then what you think then try the piece of hardware in the hole, increase ever so slightly with larger bits until your piece of hardware fits snugly in the hole. As for where to cut the holes make sure you leave enough space between the holes so you have room to work the wiring, but not to close to where the lights will go.
As for the wiring, its really not that difficult as long as you use double light socket if you want two lights, you just need to make sure you wire everything in series, AND MAKE SURE ITS ALWAYS UNPLUGGED, you go yea yea I know I've heard it a hundred time and its common sense, but hey when I was building my second light fixture I was testing it then turned it off at the switch and completely forgot it was still plugged in. Well some how I managed to touch the right wires and got a nice little shock, quick little shocks wont hurt you as most electricians will testify but never grab wires unless you know its unplugged.
Below is a simple diagram for the wiring as long as you stick with one socket, double or single the wiring is really just as easy in the attached diagram. I do have a 3 socket one over my 36 gallon tank (1 double and 2 singles) then it gets a little more complicated but even that once you understand a few principals is not that hard, and if you go this route let me know and I will give you that wiring diagram.