Airport Extreme amplifier
I would like to amplify the wireless to my shed on next to the house. What would I need to do that?
AirPort Extreme 802.11n (4th Gen), Mac OS X (10.7.4)
... What would I need to do that?
An AirPort Express or another Extreme:
Wi-Fi base stations: Setting up and configuring an extended wireless network (802.11n)
Technically speaking the terminology "amplify" is not accurate. Your existing wireless network can be "extended" in a number of ways, but its radio energy is already the maximum permitted by the FCC or whatever alphabet agency exists in your country.
An additional base station is placed a location that already receives a good signal from your existing Extreme. It creates another wireless network with its own wireless range.