Another option you may have noticed in the GUI editor is the Add Inventory button. This allows you to drag out a rectangle which will display the player's current inventory, in the same way as the Lucasarts games did. To make the inventory window scrollable, you will need to add Up and Down arrow buttons, and attach script code to those buttons to use the available functions such as InvWindow.ScrollUp and InvWindow.ScrollDown.

To see a full list of commands available for inventory windows, see the GUI Inv Window Functions and Properties section.