I used to have a few bookmarks saved for making wifi antenaes, but in the end I figured it was just far easier/cheaper/more reliable to get a roll of cable.

However if you want to stick with wireless, a booster will simply receive the wifi and retransmit. Ideally it should sit roughly in the middle of the main wifi point (usually your router) and whatever you want to receive the wifi (usually your computer). However, getting it roughly central between the two points isn't always practical. If your router isn't on the shed side of your house, a booster may provide enough boost to allow the signal to reach the shed.

A Bridge on the other hand, is more suited where you want to connect several computers at a second location (i.e. your shed). It essentially connects (aka bridges) two seperate networks together, and in the case of this thread, it makes the two networks appear as one. Wifi bridges also have the benefit of providing a physical network connection at the second location, which is always handy for older/non-wifi computers.

Which approach you use depends entirely on what you want to acheive.