This is not possible due to the Same Origin Policy.
Being able to measure the height of a page from a different site would effectively be a leak of information from that site. For example imagine framing an online banking transaction list page; by reading its height, you could determine whether the user was currently logged in to their online banking, and if so potentially how many transactions had been made recently.
There is a proposal to allow framed sites to opt in to being included in a document in a height-sensitive fashion using HTML5 seamless iframes. However we are currently a long, long way from that being something you can rely on in browsers.