I know this post is pretty old, but I had something like this custom made.
The firearms in there are just a few that I threw in when I first lit it up, wanted to see how different lengths of guns and rifles would look.
Now, its mostly handguns on top, 4 rifles/shotgun on the bottom.
Double locks top and bottom, same for some accessory or ammo storage cabinet doors on the bottom, both lockable.
Its lit from above by three led lights.
The whole build took a little over a week.
I kinda cheated though, the bottom and top portions are separate, and the both were premade, probably meant for "fancy china" or some other kind of display.
I basically scrapped most of the inside, removed the two double wooden doors on the front. Made a large frame door and hung heavy duty adjustable door hinges. (The door plus glass are pretty heavy).
I inserted heavy duty pegboard, painted it to match the wood grain (sorta, at least it wasent white like before), framed the pegboard to give it a better finish.
I now wish I would have used a router on that inner frame, but oh well. I still think it looks alright.