So I have this cool idea. I have a Lithonia Lighting 65w fluorescent area light with a cheap Caster ballast, because 65w fluorescent ballasts aren't made anymore, I thought of the idea to reverse engineer the ballast in the fixture, make a schematic for it and then order the PCB and parts for it, and make my own 65w CF ballast! Do you guys think it would work? (assuming I do everything right)

I think that if this was done right, it would work spectacularly, however:

1.) There may be chips or other semiconductor components that are unmarked, discontinued, custom-made, or just plain old impossible to get, which would make it very difficult to source these components. You may have to substitute them for more readily available components, which might require a modification of the circuit.

2.) There may be inductors (or even worse: transformers) in the ballast that are almost always custom. In this case, you may be able to order a ferrite core and wind an equivalent yourself, or you may just be out of luck.

Now, assuming you solved those “minor” problems, you are good to go. Definitely possible. Hope this helps!
 

Don't even need to reverse engineer it really, depends on how basic it is, a self-oscillating ballast is extremely easy to make, I have made and modified many with great success, you might need to wind some custom inductors though on a fairly large core but it's doable. They do require some tweaking because the current through the lamp depends on the frequency, and the frequency is determined by the current, if you find that annoying, get a self oscillating half bridge driver like IRS21531 and then you'd have a fixed frequency.

Thanks for the info. I guess with enough trial and error you can easily make a electronic fluorescent ballast.