Before roasting green beans at home, read some useful tips to make it perfect:
1.Look - the appearance of the bean will change through the roasting process. Its color, size and texture should be watched carefully.
2.Listen - two distinct popping sessions are heard during coffee roasting. These are known as the first and second 'crack'.
3.Smell - the beans will smell differently at each stage of the roasting process. The aroma should be used in conjunction with appearance of the bean to evaluate the stage of the roast.
Source: Coffee-Makers-Cafe