Making a Dark Room
Its not as hard as people think. The only thing people worry about is the enlarger… which you can actually get really cheap off of Ebay. Well the first thing you need to figure out how permanent of a room you are trying to create. If its something for your bathroom (which is the ideal place to build one) that is in a day to day use then you would have to rethink the darkrooms permanence. If it were to be permanent then I would say begin by painting your bathroom black with a matte non reflective finish.

Now for the steps that everyone considering to make a bathroom darkroom (permanent or not)- you will need to purchase fixer, developer and a stop indicator. 4 Trays, a Safelight and an opaque matte vinyl spread (preferably black). You will also need duct tape, string with clothesline clips and a rolled up towel. Attach the string in the bathroom prefferrdly over the bathtub, clothesline style. First you'll have to make the room light-proof. To do so take out all the lightbulbs and replace them with safelights. Then you'll have to seal the door. To do that you need to duct tape the edges of the door to the wall and put the rolled up towel under the door. If you have windows get the vinyl spread and cover the windows and duct tape the edges down make sure there are no spaces. There should be absolutely NO light allowed in the room. Turn on the safelight.

Once you chosen a place for the enlarger place it there and plug it in. Once you have designated a spot for the trays lay those down, now its time to dilute the chemicals. Most chemicals have dilution instructions on the back. But here they are anyways:

For every 100 ml of developer you put in 900ml of water.
For every 1L of water you need 16- 40 ml of stop bath (depending on how strong or weak you want the dilution — that depends on the paper you are using)
For every 250 ml of fixer youll need 750 ml of water.
In the fourth tray, the rinse, you can just use water. Distilled water works best, for the dilutions and the wash.
Now you are ready to utilize your darkroom. A couple of precautions:

To avoid any sort of developing mishap, I usually put another vinyl over the trays when I am developing the film, and enlarging it.
a fan is helpful to dry the pictures and to keep the room warm.
when enlarging please don't forget to put away your paper first. Any sort of exposure can ruin the quality of your photograph.
turn off all your lights (including the safelight when enlarging). When youre done then turn on the light and remove the spread from over the trays. The operation of this room is much like a standard room except you need to do more things like turning on lights covering things, etc.