Altimeters are always feet above sea level. There are also radio altimeters that provide feet above terrain.,, but the standard, in every plane, altimeter is feet above sea level.
As I recall BUF is 700+/- feet above sea level. Altimeters also need to be set to current barometric pressure. On the ground you dial/set the barometric pressure into the altimeter, and you will see the field elevation on the instrument. Once you climb above 18000' everyone uses 29.92", so everyone is set to the same setting.