Below is a good picture guide of the many methods of ramp blocking and walling with Terran:
http://www.teamliquid.net/forum/brood-war/338606-terran-walls-for-python-and-fs
Honorable Mention:
http://wiki.teamliquid.net/starcraft/Walling_as_Terran
(More of theory on why you would wall, with a few extra pointers)
http://www.teamliquid.net/forum/brood-war/338606-terran-walls-for-python-and-fs
Honorable Mention:
http://wiki.teamliquid.net/starcraft/Walling_as_Terran
(More of theory on why you would wall, with a few extra pointers)