The following are the mandatory aspects of the domain that you need to model
Your inventory schema should model the details of all products you have and their availability at the different warehouses, and the warehouses themselves. Here are some details about each of the data entities that your schema should model.
Books: Every book has a title, author (one or more), and an ISBN (a unique number that is used to identify the book). Clearly you should model the selling price of a book and books may also have discounted prices.
Books are organized by categories (e.g. fiction, drama, fantasy, history, etc.), so that they can be easily searched. Any book typically also has a set of keywords that describe the contents of the books. You should model both the categories and the keywords.
Music: Every CD has an album name, an artist (one or more, may be a group identified by a name), a recording company, some unique identification (like the ISBN for books), and a selling price. Just as books, CDs are also categorized by genre (e.g. rock'n roll, jazz, classical, etc.). Further CDs can be of various types - singles, albums, commemorative editions, etc.
Availability: Each of the books and CDs can be either in-stock or out-of-stock at the different warehouses. You will be definitely interested in the quantity in stock at your warehouses (for each product), so that you have an up-to-date availability information.
Warehouses: Each warehouse has a particular location (street address, city, state, zip code) and contact information (telephone number, fax number, manager's name). Warehouses usually have an estimated capacity in terms of the number of employees, volume of business, etc.
Optional modeling: In addition to the mandatory aspects of the domain, you should add about 4 attributes of your own. You are welcome to visit any of your favorite online stores for ideas on additional attributes to model in your application.