For a treatment of buildings with examples (not only for the spherical building, but for other notions as well) I recommand :
Abramenko, Brown, Buildings, Theory and applications, GTM 248, Springer 2008
Dasgupta, Teitelbaum, The $p$-adic upper half plane, in $p$-adic geometry, Lect Ser. 45, AMS, 2008 (for the case of ${\rm SL}(2)$)
Garrett, Buildings and classical groups, Chapman & Hall, 1997.
Ronan, Buildings: main ideas and applications. I Main ideas Bull LMS 1992
Ronan, Buildings: main ideas and applications. II Arithmetic groups, buildings and symmetric spaces, Bull LMS 1992
