How could i make a Npc Dialog giver?

While http://robloxdev.com/articles/Shop-Dialogs is a pretty straightforward answer by Crazycat4360, there are alternate ways to do this. There is, of course, the hard-to-do Billboard Gui methods, and then there is game:GetService("Chat"):Chat(script.Parent, "--[[ Your text in the quotes --]]", 1 --[[1 (blue), 2 (green), or 3 (red)--]]) (http://wiki.roblox.com/index.php?title=API:Class/Chat/Chat), and then opening a custom-made ScreenGui for the chat feedback. Then, after the player buys said power up, you can easy give it to them.