If you went to college, particularly in the 1970s, you probably saw dorm rooms and student union offices where some of the book shelves, seats, record album storage shelves, coffee tables and even lamps were constructed out of commercial plastic milk crates. Most of those milk crates were probably stolen from the backs of local grocery stores and restaurants, which can get you into trouble with law enforcement. However, some companies have wised up and now sell authentic plastic milk crates to consumers. Now you can make a real milk crate book shelf while staying on the right side of the law.
Milk crates, designed to carry bottles of milk from dairies to grocery stores and restaurants, were originally shallow sectioned boxes made of wood or galvanized steel. The tough plastic crates are actually high-density polyethylene resin. Milk crates are the ultimate modular storage unit -- you can always take your milk crate book shelf system apart for transportation, or reassemble it differently if you need to change or expand the original setup.
Be sure to use real crates for a milk crate book shelf. Discount chain stores sell plastic storage units in the shape and size of milk crates, but these are usually flimsy, don't interlock well (or at all), and have neither the strength nor the durability of the genuine article. Several companies, particularly containerstore.com and duluthtradingcompany.com, now sell authentic milk crates for the general public. You might also be able to buy them direct from a local dairy, or ask politely at a grocery store. Be careful about just taking them. Milk crate theft is a crime, with serious legislation in some states. Some companies lose hundreds of thousands of crates per year -- they are sold to recycling companies.
You will also need some plastic cable ties, which you can get at Radio Shack or any place that sells audio and video equipment. Even some drugstores have them now. Depending on how permanent you want the milk crate book shelf to be, you may want to get re-usable Velcro cable ties, although these are not as strong.
Decide how large you want your milk crate book shelf system to be. A real crate can safely hold about 35 pounds. Arrange your crates in any way that looks attractive and is easily accessible to you. Fasten the crates together with at least two cable ties -- you may want to use up to four.
You might like to spray-paint your milk crate book shelf in attractive colors after assembly, or decorate it with Krylon Fusion paint. Some people drape fabric over milk crate furniture, while others leave it exposed. The common milk crate has a cozy, nostalgic value for many people, evoking memories of vinyl record albums and student days.