make sure there's plenty of room on for them to stand, it's a half life glitch, not totally your fault. What happens is they didn't put into the engine an ability to make you go smoothly with the elevator, so when your being constantly lifted with the elevator, it puts you inside of it. There's a glitch like that in the actual half life game, the elevator that goes to the surface about 1/4th of the way up
to fix it, just make sure there are railings or an invisible func_wall for the railings, and make sure it's big enough for 2 people to stand on easily