why not build a raspberry pi laptop
There are these devices that are meant to connect to a mobile phone.
they usually use some sort of USB, and some sort of HDMI, so interfacing it to a desktop should just be a matter of using adapters.
yes but if you add a tft screen and a battery you will have your own raspberry pi laptop
That is true, I was thinking about doing this before. This guy did it, it isn't exactly how I would do it, but it's worth a look.
http://www.geeky-gadgets.com/awesome-pi-to-go-raspberry-pi-mini-laptop-created-21-12-2012/