Folder Creation in the "~/" of my website

hi all, i am trying to dynamically create a folder in my website directory heirarchy . it gives me error as i do not have the permission to do the same thing. The error says  "Accesss Denied"
path = "~/" + NameBuilder.ToString();// it has "test" in the namebuilder string. Directory.CreateDirectory(path);

what shall i do to resolve the issue please suggest !

also tell me if there are any security hazards
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