Layouts?

What are the layout dimensions? i'm going to make a layout in photoshop is there anything i need to download?

I open a document at 800 x 800.

My layouts usually have a top bar which reaches 100%, but the layout is usually 500-600px.

Have fun making your layout ;)

I usually do;
width; 956px;
height: 700px;

I usually do 800px x 700px. I then make things bigger when I code depending on the layout.