How can i give a building with shop sharing upgrade selling?

I know you can sell units and items on a building with shop sharing

but how can a building with shop sharing sell upgrades?

Just give the shop building upgrades? Or make a dummy item, and then make a trigger that reacts on when the dummy item is sold.

buildings with item sharing cant have upgrades that way.. i think its an ability or something... and if its an item, then id need a different item for every level.

The only way to do the upgrading by dummy items or units

i downloaded the .slk, put it in the right folder, even imported it into my map

how do i make the units be able to sell upgrades?

Try this:

Create an Item called " Upgrade Damage " and remove all abilitys give it an Upgrade Icon and a description.
Now go to your Shop which will sell the "Upgrade" and add your created Item to the list.
Then go to Trigger Editor and do this:

Events
Unit - A unit Sells an Item
Conditions
(Item-type of (Sold Item)) Equal to "Upgrade Damage" (Item)
Actions
Player - Set the current research level of Damage Upgrade(Create the Upgrade u want first) to ((Current research level of Damage Upgrade for Player X) + 1) for Player X


Ok try this if you dont understand this ask me!

well, as the level increases, the upgrade gold cost should increase... is it possible to change the gold cost inside the trigger as well?

Not in the trigger but u can do it with the Upgrade-Editor.