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 halp plan, 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

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