To link 2 or more buildings together we suggest using the Ubiquiti brand products. 2.4ghz is going to be a little cheaper in cost over the 5ghz. 5ghz will work better in an urban environment. You will need 2 of these wifi points. Wifi point 1 will be the base where the signal is coming from. Wifi point 2 would be the remote building that needs internet.
Ubiquiti NanoStation locoM2 2.4GHz
Or, the 5ghz models… Ubiquiti NanoStation loco M5
Ubiquiti Nanostation NSM5 (High Power Models)
A great tool to see what equipment you will need to get signal where you need it at.