This MenuFramework library allows to simply create inventory interfaces. This includes menus in the player inventory, menus in all kinds of top inventories (Chest, Hopper, Furnace, Anvil, ...) and Trader Menus.
Example from my own Server, in combination with resource pack:
Example of a menu from a
shop plugin i currently make.
The player inventory is filled with a navigation menu that modifies the top inventory. Again, a resource pack was used.