Gage's office is located on the fifth floor despite the professor's bad leg. He chose the fifth floor because of its "en-route-ness" to the Ravenclaw Tower. He also chose it because of the prime pickings to hear the music wafting from the designated classroom. He arrives at his office with the help of a spell (which he adamantly verbalizes as "Giddyup") that causes the stairs to act like a Muggle escalator.
Outside, below his name plate and declaration of specialty there is a place for a sign to go but the professor hasn't added it yet.
Inside, one will find an interesting blend of the magical as well as the muggle. A Foe Glass hangs to the left of Gage's chair, while a Rock Band guitar controller looms off to the right a little higher on the wall. A modern muggle centrifuge sits upon one end of his desk (an antique mahogany moderately stained with cherry) while a shrunken apothecary barrel directly from Diagon Alley sat at the other. Inside the barrel was a large assortment of both muggle and magical candies for his and his students' perusal.
Two large, floor-to-ceiling bookcases lined the rightmost wall. Upon these shelves one could find a great many books about potions, the Dark Arts and their defense, demonology, Arithmancy, cooking, jokes (practical and verbal), and the list goes on in variation between the magic and non-magic varieties. There are a couple of books therein about magical eugenics, or blood purity, but these were purchased so that he might become more aware of those opposing his demographic. There are also many comics and whimsical works for leisure reading there as well. Occasionally, there is a break to separate books into specific genres. Within these spaces are several items: a mortar and pestle, a cup full to bursting with quills, a flower pot full of floo powder, and a bucket of Gobstones.
Another cup full of quills can be found on his desk, as well as a set of potion phials containing different color inks. Two smallish chests line the left side of the wall and contain ingredients and an impressive potions supply, respectively.
In front of Gage's desk and comfortable office chair are two similarly comfortable armchairs, and a coffee table adorned with a few current publications regarding some of the professor's interests.
Come on in and talk to him (in a separate thread, if you would, please) if you've any questions on an assignment, a potion, extra credit, or an impending finals week dilemma...
Just be wary of the various joke items hidden about. Gage tends to be quite the practical joker given enough time and opportunity.