Gatehouse

Noun

 * 1) A lodge besides the entrance to an estate; often the residence of a gatekeeper; also a dwelling formerly used as such a residence.
 * 2)  A fortified room over the entrance to a castle or over the gate in a city wall
 * 3) A shelter for a gatekeeper.

Thesaurus
Nissen hut, Quonset hut, booth, crib, hut, hutch, kiosk, lean-to, outbuilding, outhouse, pavilion, sentry box, shack, shanty, shed, stall, tollbooth, tollhouse

Alternative forms

 * gate house