Why not just use the default shop? That said, I don't know what the setup is going to be like (just one item on the screen at a time? Or a few?) and how big the items basically are.

---------------------------

With just one, it's a bit easier to set up. You just need to display the first picture at whatever coordinates you want, and capture the keys that the player is going to need - namely left, right, cancel, and enter. You then just change the one picture accordingly, based on whatever item you're on.

PSEUDOCODE:

<>Display picture of item (probably with price right on the picture)
<>Set variable [0055:ItemNumber] to 1
<>Start Loop
___<>Key input processing -> [0001:KeyCaptured]
___<>Comment: -----------------------------------------------
___<>Branch if Var [0001:KeyCaptured] is 2 (Left Key)
______<>ItemNumber = ItemNumber - 1
______<>
___:End
___<>Comment: -----------------------------------------------
___<>Branch if Var [0001:KeyCaptured] is 3 (Right Key)
______<>ItemNumber = ItemNumber + 1
______<>
___:End
___<>Comment: -----------------------------------------------
___<>Branch if Var [0001:KeyCaptured] is 5 (OK Key)
______<>Comment:------
______<>Comment: Buying Subroutine Goes Here
______<>Comment: Check for amount of gold, add +1 item based on
______<>Comment: ItemNumber variable, take away gold, then continue
______<>Comment: ------
___:End
___<>Comment: -----------------------------------------------
___<>Branch if Var [0001:KeyCaptured] is 6 (Cancel Key)
______<>Break out of loop
______<>
___:End
___<>Comment:-------The Part Below "wraps" the item list around-----
___<>Branch if Var [0055:ItemNumber] is 0
______<> ItemNumber = Maximum number of items
______<>
___:End
___<>Branch if Var [0055:ItemNumber] > Maximum Items
______<> ItemNumber = 1
______<>
___:End
___<>Comment:-----Picture changes happen here, add how many you need-----
___<>Comment:---Yes, picture will "change" even if you buy something instead---
___<>Comment ---of moving (of course, it will "change" to the same item thing)---
___<>Branch if ItemNumber = 1
______<>Change picture to "Potion"
______<>
___:End
___<>Branch if ItemNumber = 2
______<>Change picture to "Sword"
______<>
___:End
___<>Branch if ItemNumber = 3
______<>Change picture to "Shield"
______<>
___:End
___<>
:End (Loop)

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I just threw that together. I'll have to do more when I get home..