Presumably you're talking about a ridge tile on a hipped roof. The bottom tile is often fixed using a hip hook (which is a decorative feature as well) attached to the hip rafter. the tile is held by that and the usual sand & cement/mortar used to bed and point the tile. Alternatively a strip of expanded metal (mesh) can be nailed to the hip rafter to give the sand& cement/mortar a better grip.
JD, March 2009
