HOW to DESIGN, BUILD and TEST SMALL LIQUID-FUEL ROCKET ENGINES
Risacher.org, 29 December 2011
http://www.cientificosaficionados.com/libros/cohetes.pdf [PDF, 6.3M]
This excellent book, written by Leroy J. Krzycki in the 1960's provides a good theoretical and practical overview of developing your own liquid propellant rocket motors. Although dated, it provides timeless theoretical coverage in an understandable fashion. It covers all aspects from the motor to a suitable test system.