Has anyone ever made FFT for MT4 or know if it is available?
I Think it would be nice to have that to get more accurate periods for other indicator inputs.
Or is there a simpler way to get periods? (some web site or service...)

I'm coder myself, but I'm not very fluent in the math theory, maybe at least I could get help with that.

I'm just busy to write a MT4 interface to FFTW library. It is still work in progress. Anyway, can you describe what is tha application and how you want use FFT? The I can perhapse write interface for you. Note that this is all done in C++.