How do you know how many studs tall and wide your place is?

   I am currently working on a project that needs to be a certain size. The problem is, I am not sure how I would know how many studs tall and wide the project is.

The easiest way would be to group everything into a model. Ever thought about the highlighted rectangle when you're dragging a model around? Someone recently showed me a list of methods that can be used on models, one of which being the dimensions of that rectangle.

so basically just use a script to print the selection box size into the Output window.

You can look by going to the size property inside a brick. Go to the brick and scroll around it until you find size, those coordinates tell how wide and tall the brick is.