Minim recreate waveform from FFT bins

So I've got a working FFT example, and a working additive synthesis example, but can someone help me connecting the dots between additive synthesis and the output of the FFT? The FFT is set to 1024 and kicks out 512 bands, for a 44.1khz signal. How should I configure the FFT output or add sines together to recreate the waveform from the FFT bins? I guess I can't get the scale right? Thank you!