Rick Campbell KK7B has written several articles on direct-conversion receivers; the articles appear in QST and other places I think and he wrote a detailed section of Experimental Methods In Radio Frequency design about DC receivers.
Incidentally, EMRFD is the experimenter's Bible; no home-brewer should be without a copy.
Here is an article by KK7B;www.arrl.org/files/file/Technology/tis/info/pdf/9208019.pdf
It explains the design in step-by-step form.
I think that kits are available for some of the designs; Kanga, for instance, has the micro R2;http://www.kangaus.com/receivers.htm
and FAR circuits has just the PCB;http://www.farcircuits.net/
Building one module at a time and testing it is a very good technique; here are modules of a DC receiver based on the EMRFD section;http://i47.tinypic.com/2v2ch9f.jpg
You will require some test equipment; a signal generator and an AD8307 microwattmeter will be a start and construction of the wattmeter (kits are available from KA7EXM and others) will be good practice.