Building a simple Natural Radio Receiver is not too difficult for anyone with basic construction skills. Most of these circuits use readily available parts and the layout is not overly critical. Just remember that since these circuits are high-gain and the input impedance is high in the case of E-Field receivers, to keep the input and output sides of the circuitry separated.

The BBB-4 Steve McGreevy's BBB-4 (BBB = Bare Bones Basic) is relatively easy to build and is the product of many years of experimenting and research. http://www.auroralchorus.com/bbb4rx3.htm

Dual FET Receiver Here is a receiver design by Eric Vogel that uses a dual FET front-end for a higher input impedance, has passive filters, a separate record output and runs off of a single 9v battery. http://home.flash.net/~evogel/ev-wr1.html

ELF Monitor with AGC & Hum Removal This page contains some interesting design ideas for a fairly sophisticated ELF receiver. http://www.techlib.com/area_50/elf_receiver.htm

Radio Waves Below 22 Hz Renato Romero's site has quite a few diagrams of Natural Radio receiver circuits along with many design ideas. http://www.vlf.it