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.
This PDF will outline how to set up the link on the wifi. You want just the first few pages for PTMP (Point to Multipoint). I suggest setting the wifi points up this way, makes it very easy to add another wifi point down the road.