You can roast coffee beans at home, very easy and cheap, using an Air Popcorn Popper.
You only need an Air Popcorn Popper with a recommended design (see the image below). I am using this one here. With a design like this, you don't have to "hack" or destroy the machine, so you can use it and for Popcorn.
Buy Green Beans of your choice and when you want to roast them, put in the popper a small quantity and power it up.
In 2 minutes you should listen the first "cracks" of the beans and in 5 minutes these cracks will be more often. You can stop the roasting if you want your coffee be light or let them for 2 minutes more, if you want your coffee more dark.
When finish, turn off the machine and put the beans in a dish and let them cooling. You can now use a grinder or a blender, if you don't have a grinder to grind the beans.
Store the coffee in an airtight glass jar, but don't seal the jar tightly immediately, keep it a bit open for 10 hours and then seal the jar tightly and keep it away from direct light.
Use this coffee for a week. After that, your coffee will not be so fresh. Measure the quantity, so you can roast enough beans for your week's coffee.