Coming up with a common set of descriptors for beer styles is more difficult than it sounds since there are so many styles to compare, each with a different character. One way to do it is to describe ranges for physical attributes like Original and Final Gravity, IBUs and Color, but this is really only half the story. To try and give you the other half, I illustrate each description with a commercial example and a baseline recipe. In each recipe, I identify the appropriate malt extracts and specialty grains, hop varieties, yeast strain, and fermentation conditions. I have grouped the styles by Ale and Lager according to the yeast; and sorted them on the basis of color and body to progress from lighter beers to heavier.
The recipes use both extract and specialty grain because this provides the most insight into the beer style for the beginning brewer. If you do not have access to a particular specialty grain, then substitute an equivalent amount of an extract that contains that grain. For example: Amber malt extract instead of Pale extract with Crystal 60 malt or Dark malt extract instead of Pale extract with Chocolate malt.
NOTE: All recipe calculations for OG and IBUs assume the use of a 3 gallon high gravity boil for a 5 gallon batch. Depending on the type of extract used, the actual boil volume could be as high as 4 gallons. You may want to recalculate your gravity and hop additions for your own equipment. All-grain versions of the same recipes assume 6 gallons of wort being collected and boiled to produce the same 5 gallon batch. Hop boil utilization will increase because of the change in boil volumes, so be sure to use the calculations presented in Chapter 5 - Hops, to account for the increased utilization and adjust your hop amounts accordingly.