I am struggling to find a way cycle the Build Modifier. I have tried to make it work with the F curves and the NLA but without success. The Build modifier is controlled by the timeline frame number and the length of the effect. When I cycle the keyframes in the fcurves, it cycles the start frame so when the timeline bar has past the keyframe once, the cycle goes backward whilst the timeline bar continues forward. The same happens for the NLA. The only solution is the video editor but that is not very practical.
I was hoping that somebody would have a smart formula to be able modify the start and length so that looping can occur.