Garage Doors - Some Questions On How

[scar tissue]

Last night, I had a dream. In this dream, I pictured a mod project for a HaloCE Level that I know everyone (well, maybe only gamers who like the old games) will enjoy.

I don't want to reveal the project, but I do have to bring up one aspect of questions.

In this mod, I am planning on placing two garages, each holding so many warthogs (I haven't decided on an actual number). My problem is, I've never made working doors before.

My first question is, how would I go about making a working garage door that opens up and down?

My second question is, how would I make the doors only open when someone is coming out of the garage and not open when they are trying to go in?

Any help would be much appreciated. Thanks in advance.
(And Happy X-Mas Eve )

[p0lar_bear]

Make a device machine that operates automatically, and when you place it in Sapien, make it one-sided only. Which side is the openable side, you will have to find out during playtesting.