The smaller home roasters are based on the air popper design for the most part. These are fluid bed machines - they use hot air to roast and move the coffee. They roast a small amount of coffee at one time, enough for one or two people, and are relatively in expensive. The ideal time range for an air roast is 8 to 12 minutes. Batch size can range from about 3 to 4 ounces. Four ounces of green coffee gives you about 5.25 scoops of ground coffee - that is just over 26 ounces to 42 ounces brewed coffee depending on how strong you like your coffee.
Air roasts tend to develop the brightness of a coffee, drum roasts tend to develop the body more. Some brewing method, like espresso, tend to favor coffees with more body instead of brightness, but there are really no hard and fast rules when it comes to coffee roasting.
An important concern with air roasters is that all of these small machines are effected by two things; 1) line voltage and 2) ambient temperature. Line voltage can vary 105v to 125v from house to house and even on the same outlet depending on what else is running. (I know this doesn't perceptively affect your toaster -so why should it affect a roaster? I don't know why, I just know it does.) Ambient temperature of the air will effect how hot the machine gets, so if you roast outdoors and it is much cooler or much hotter than room temperature, the roast will go much slower or faster. A very low ambient temperature will require the machine to work harder to reach roasting temperatures. The roast times as a result may be much longer than ideal.
Here are some helpful links: