Green coffee beans are available in some coffee shops and many web shops, eBay is also a great place to buy unroasted coffee.
Coffee may be roasted in many different ways, at home you may use the stove or a frying pan. Light roasting may be done indoor. However, roasting on the darker side causes a lot of smoke development. Roasting outdoor on the gas grill saves a lot of trouble associated with smoke and chaff in the kitchen.
You can use a regular roasting tin and spread the green beans evenly as one layer. In this way you may roast at least half a pound in one session. In an emergency situation you may even roast coffee beans on a sheet of aluminum foil on gas or charcoal grill.
I usually turn the heat to maximum and leave the grill open for a couple of minutes, this will dry the beans before the roasting process starts. During roasting you can keep the grill closed and open it every 4-5 minutes, shake the tin to spread the heat and close the grill again.
Continue to shake the tin or stir the beans every 4-5 minutes and keep up the heat.
As the temperature inside the beans reaches 390 F (200 C) they crack and make a popping sound, almost as popping popcorn. After this first crack the coffee is light roast.
When the core temperature of the beans is 440 F (225 C) they crack for the second time. After this second crack the beans are dark roast with a dark oily surface.
How dark you roast the coffee is a matter of taste and the different popping sounds indicate how dark the coffee has become when the grill is closed.