Hello, I am looking at making a tower defence game and I have been unable to get a grid and building system working properly.
Anyone have any examples or ideas that could help me out?
I am not sure what you expect in terms of ‘ideas’, what you are trying to do sounds simple enough.
You need to look at detecting mouse position across a given plane (probably using raycasts). Look for a given input from the user and instantiate your towers at that position.
As usual Unity - Scripting API: will explain any terms I posted you’re not familiar with.
Please remember this is a scripting section, people in here want to help with scripts, not your lack of script.
EDIT: Take a look at: http://forum.unity3d.com/threads/50108-Griddy-Unity-Grid-Toolkit-(Free-Open-Source-Incomplete)
Sadly there is no download link on that last link you sent 
Thanks for the advice ill check that out 
Here is: https://github.com/nickbreslin/Griddy
Click in ZIP button, and get the whole project.