The ARRL handbook is a good reference for home construction of other amplifiers. Kits are also available at times. Check the classified advertisement section of QST or other ham magazines for kit suppliers or for used amplifiers. As I said before, you do not need high power to listen for eme signals. Listening is a good place to start your eme experience.
Signals are very weak echos reflected from the moon's surface.
Signals are usually at the noise level, or even buried beneath the noise, ocasionally rising above the noise for brief periods. Hard listening and mental concentration is required to pull the signals out and identify what is being sent. Most commercial receivers are not good enough, but a relatively low cost preamplifier can fix that. Your well designed antenna must be pointed at the moon . In most locations, ground gain can often give some signal enhancement when the rising or settig moon is below 12 degrees of elevation.