Drawing shapes and taking measurements

I'm looking for advice on how to do the following:
Using PHP and Jquery, I need a page that allows you to upload a PDF/Jpg and measure areas of it.
We plan on uploading plans for houses and tracing them to get measurements like this:
http://www.databuild.com.au/help/index.html?graphicaltakeoff.htm

The script will need the ability to draw rectangles and lines then store the measurements in SQL.

Can anyone suggest a library or good starting point?

 

You could make something like this by using the HTML5 canvas. Have a read of this article: http://diveintohtml5.info/canvas.html

You could easily attach some call back functions to work with the backend. http://api.jquery.com/jQuery.ajax/

Hope it helps!