What do you mean by WiFi? You mean an actual internet provider that is wifi? Those usually involve external antenna's on the buildings. If you just mean to implement a "simple" wifi network that's independant, a simple wireless access point would work fine.

Depending on your location of course, but i doubt ISP wifi would reach you indoors. As it usually involves line of sight to the towers. (Unless your area has setup an "area" hotspot").