Hey. I'm a 12+ years professionnal .NET (C#, VB.NET, Xamarin, ASP.NET) developer.
I know exaclty what you want. You need a special folder like DropBox, Google Drive, SkyDrive... where you put your files in, and they'll get processed and converted to your special zip format. If, in the contrary, a file from your folder gets out from it, its converted to standard zip format.
I can do this quick and good. I'm sure you'll be happy with the result.
PS: my skype is nadjib213, I'd be happy to discuss the project with you.
S uvazheniyem,
Nadjib Bait