Many folks keep some of their collectible guitars in display cases or guitar cabinets that may have a glass front to allow viewing of the instrument. However these cases should have a built in humidity control system as it is vitally important to maintain the proper level of relative humidity for your guitars.
When storing guitars, one of the most important consideration is the environmental conditions that the guitar will be subject to during storage. This would include extremes of temperature and most importantly, relative humidity.
This is particularly important with acoustic guitars who's body is solid wood (verses laminate or composite) or guitars with a solid wood top. Solid body electric guitars and all laminate body acoustic guitars are not as sensitive to the environment as the solid wood acoustics, but will still be affected.
Wood is very susceptible to relative humidity (basically the amount of moisture in the air). Too little humidity and the wood drys out and your guitar can develop any number of problems. Conversely, if your guitar is exposed to conditions where there is too much moisture in the air, the wood can swell and cause different problems. Here is a link Humidity and Guitars that tells you more about how humidity can affect an acoustic guitar and the optimal humidity range.
Many people choose to store their guitars in a hard-shell case with either a sound hole or in the case humidity control system. However, if you have quite a few guitars, it might be practical to store them in a dedicated case or cabinet, as long as you have a way to control the temperature and relative humidity levels inside the case or cabinet.
If you can create a weather tight seal with weatherstripping and tightly closing doors, you could use some sponges in containers to provide humidity along with a hygrometer to monitor the humidity level and add or subtract water from the sponges as needed.
Or you could use a small electric humidifier with a built in hygrometer which you would set to maintain the humidity at your desired level (between 45% and 55%). Of course you would need to be able to get the power cord into the case or cabinet.
If you don't want your guitar "rack" to be sealed, you may want to consider a room humidifier to maintain the optimal humidity level in the room where your guitar rack will reside. Again, there are many models that will automatically maintain a pre-set humidity level.
Aside from taking steps to insure optimal relative humidity, you should also consider the location of your storage cabinet or rack or case. It's best not to expose anything to direct sunlight that you don't want to fade over time. If you live in a climate where there can be temperature extremes, you might not want to locate your storage unit on an outside wall.
One other consideration for security that I would keep in mind. Guitars can be valuable and if a burglar ever breaks into my home looking for something to steal, my guitars are the last thing I want him to see. You might want to locate the storage unit in a part of the home where it will be least likely to be found by burglars looking for valuables.
Finally, be sure your guitars are supported inside the case in a manner that does not put undue stress on the neck of the guitar. You don't want any pressure in either direction that could warp the neck. Store the guitars so that the necks are not touching anything or so that the guitar is suspended freely from the headstock - with no pressure on the neck itself. For long term storage, I would recommend loosening the strings as well.
Good luck with your storage unit!