I think what you are referring to is a powder magazine. The term is primarily applicable to business rather than the presumably smaller amounts stored by private individuals. I suspect that you would find the requirements somewhere associated with the explosives branch rather than the firearms act or criminal code.
For small amounts and private individual, I think common sense applies; somewhere cool, secure from theft and presumably a bit separated from houses and dwellings. Also would suggest not making the private magazine, overly strong since that contains an explosion and creates a bigger bang, where ignition to occur
cheers mooncoon