I don't think Roblox supports standalone builds (aka people need the Roblox game to play your game). Also, remember the jam is 1-Bit, meaning you can only use 2 colors at a time. Not exactly an easy feat to achieve in Roblox.
a ZIP file would still mean some1 will have to install the robolox player.
i think your best option here is to upload the robolox game to some kind of a cloud based platform, search google i dont know if i'm allowed to write it in here :)
