It is highly unlikely that you will have to acquire a building permit for this type of project, unless you decide to do any kind of plumbing or electrical wiring. When in doubt, be sure to check your city's building codes.
Not only can you find some good looking corners shelves that could possibly hold your stereo speakers, but you can also find them in a floating shelf design. A floating shelf is just a shelf that attaches to the wall via a bracket that has two or three rods protruding outwards. The self simply slides onto the rods, and then locks in from an access screw or hex nut located on the bottom of the shelf.
The final consideration when using prefabricated garage shelves, especially those designed for heavy loads is that you find some way to attach them to the wall, or create some other form of support that will prevent them from tipping and creating a danger to friends and family members.
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