All aluminum is not created equal. According to Metallurgical Consultants, aluminum alloy can be divided into nine different groups. Aluminum's strength and corrosion resistance is altered, depending on what metals are added to the molten aluminum. Alloy numbering begins at 1,000 and ends with 9,000. For example, all alloys that fall within the 3,000 designation has magnesium added in.
The sides can have different sizes. For example, a cross section can have one leg of the "L" 2 inches long and the other leg 1 inch long. The size of the legs is really up to you. Determine your application and needs, and size up an angle section accordingly. Many industrial materials suppliers stock a variety of off-the-shelf sizes, and more than likely they will have the size you need.
Here again, thousands of different thicknesses of the legs exist. For example, you may specify a shape with each leg being 2 inches long. However, you can also specify that each leg have a thickness of 1/8 of an inch. Conversely, you can specify one leg having a thickness of 1/8 inch, while the other leg has a thickness of 1/4 inch.
Most aluminum angle stock has an angle of 90 degrees between the legs of the "L." Other shapes may the the angle set at 30 degrees, so it looks more like a "V." Skewed angles of the legs are not common, so you may have to hunt around for a supplier that stocks a non-90-degree angle.
If after looking around you still can't find the exact shape, thickness or alloy you need, aluminum companies can custom fabricate anything you want. For instance, the aluminum Company of America (ALCOA) is a large aluminum fabricator. ALCOA has a customer service contact person who can address your needs. For a company to make a custom shape, thousands of dollars have to be invested to make one-of-a-kind tooling. Be prepared to absorb the cost of tooling, along with the cost of transportation to your facility.