Unmanned Shop

Can anyone tell me how to create a building that a player can purchase units without having to be nearby the building?

Thanks

I imagine there's an ability that allows a unit to sell an item, and the ability could be modified to allow a very large range, larger than the whole map... At least I think that's how it should be done....

Sell Units, Shop Sharing, and the units under Units sold seems to do the trick. Thanks anyway.