Not exactly what you are looking for, but....

...Charlie Comstock's "Up the Creek" column, in the April/Jun 2009 issue (pg 100) describes how he built both a vertical lift up hatch (on drawer rails) and a swinging gate bridge. Seems like the vertical lift hatch could be modified to meet your needs. It's available here: http://model-railroad-hobbyist.com/sites/all/themes/common/MRH_downloader/mrh_downloader.php?xmlpath=.%2F&xmlsource=MRH_issue_002.xml

lifting section

Here is my lifting board, it spans the entrance to my layout room, although with the board at 60" high I normally duck under. To complicate it I have two levels crossing it! When fully it up it just overbalances in the open position to stay up. When down both ends rest on wood supports, I don't rely on the hinges to hold the level. The lifting end has wood alignment blocks to locate it and gate catches to lock it down. If used more often metal pins may hold better accuracy.  A club I belonged to built a swinging gate, it took up more room, but since it swings couldn't be dropped too fast and was more natural to use, just like a door.

Here it is when lifted