Many people think they need a large space in order to grow marijuana. They picture plants 5 feet tall, spreading out several feet — those plants are real, but so are plants growing in 8 or 12 inch containers, in a row, under 4 T5 fluorescents in a small closet (or even just a part of a closet), or an armoire, or even just a shelf!
Another way to grow in a small space is to use 4-inch rockwool cubes, which can be purchased online or an indoor gardening store. Place about 4 plants per square foot, or you could let the individual plants grow larger to fill out the space and get the plants ready for flowering.
When the plants have grown just a little bit, place them on a timer — giving them 12 hours of UNINTERRUPTED darkness each day, make sure to fertilize — and in 6-8 weeks you will be harvesting bud!