What is needed to build a delay box for Drag Racing?

A Delay Box is a little complicated to build from the look of what I saw at http://www.biondoracing.com/DelayBoxes.shtml#MEGA200 perhaps you would be better off purchasing an older model.

There is a "Dedenbear RTD7 Reaction Delay Time Box, Race, Racing" on eBay sale ends 3 July.

Hope This Helps.