How to make the dialog for an Item Forge?

Hello I am trying to replicate the item forge system of Taerom Thunderhammer but for a new smithy in the City of Baldur's Gate. I am having no luck in reproducing a new bug free item forge dialog in Baldur's Gate Arms and Armour Emporium; see for more information: https://forums.beamdog.com/discussion/71447/baldurs-gate-arms-and-armour-emporium/p1


I have a whole bunch of item upgrades created but now I am trying to get a working dialog to forge these item upgrades. For example I have an upgraded Longsword +2 'Varscona' SW1H06 via Longsword +3 'Varscona' OSW1H06+ which requires gold and some other valuable items to upgrade from the original +2 version.

I have not done custom dialogs mostly outside of Item Descriptions so this area is a bit new to myself and any help and or guide would be greatly appreciated. I am looking for any help and or guide to make a proper item forge dialog; the item files are ready to go it is just I am stalling in how to construct the dialog.