Depends on many things really, but first things first... if it is not legal where you are then a garage is a big, big, big DONT DO IT!.. Also depends what you want, if you want upto 14g thwn a couple cfls, basic soil, nutes and seeds will get you there. If you want to smoke the dank over the next few years then you should be looking into a hydro grow with 4 1000w hps lights, a c02 system, ozone generator (optional) and a 3m by 2m tent... there is a reason weed costs the same as gold. You can grow it, or you can grow it well