When you boil it down there are only two different types of wine cellars - passive and active.
A passive cellar is one that is not actively climate controlled.
An active cellar is one that is climate controlled so it behaves like a big walk-in refrigerator.
Whatever your approach is to your cellar, remember this one idea:
The ideal room conditions for long term wine storage consist of a constant temperature between 50° and 60° F with 50% to 70% relative humidity.
Ideally, a passive cellar will maintain constant temperature and humidity year round - like a cave in France. Basement spaces that are ideal for passively storing wine are usually below grade and surrounded by earth on 2-3 walls. If the room that you choose to store your wine in does not have a 6 degree temperature swing in a twelve month period and falls into the right humidity range, all you need to do is add some racking and viola, instant wine cellar.
If your room is not in an ideal spot, you are going to have to actively control the conditions of the room with insulation, a vapor barrier, a cooling unit etc. To build a room specifically for these conditions you'll want to take extra care during construction so that you don't eventually damage your storage space or overwork your cooling unit. Nothing is more heartbreaking than a failed wine cellar.
Proceed to Part 2: Cellar Construction