Console

view sourceGet source

hide source

insert layoutclose

Construct your layout using the wysiwyg tools. After you're satisfied, click the 'Get source' icon first, and then click the 'view plain' link at the top of the popup.
Simply copy the source code and paste into your own custom page.tpl.php file. Theme appropriately.

(NOTE: custom sizes will require slight fiddling with widths in style.css. Custom size functionality in builder a future possibility.)