Do you want to make an item for a npc..? or make your own mall..?
If you already have the Npc. find and download the Gmaddon tool. there you can look up items and add them to your npc.
Best thing is :
1. Make your items in your sql tables not in wow-v or such websites...when i was a noob i used wow-v cuz its easy but sql is more cooler you can add extra things etc
2. Make your npc in your sql table dont download one premaded and edit just make yourself one
3. To add items to vendor add them in vendors not in game with the command, trust me its more better to add em manually
Now for a mall :
1. After u finished to make all custom items and npcs and gameobjects and all you need for your town/hall/city/mall find a place that u like
2. Place there the gameobjects too make it look stylish than spawn the vendors make some tables some chairs too look really stylish
3. After youve doed that take a WarpNPC Source and edit it and add a line with the teleport to these custom city or if you want you can make a portal or a quest to give u something to enter that city.
Now if you do that youl have a great mall like mine