Good luck with that, About six months ago, I spend a considerable amount of time trying that... The absolute best solution I came up with, which I didn't find acceptable, was to buy up broken/new laptops and frankenstein them - it can be done that way but I decided not to go there. As far as doing a "new laptop build" I never found any sources that would allow me to do my own laptop build.
If you do happen to stumble across one, give me a shout - I'm still interested in the prospect
There's a small number of barebones you can buy from various places (xoticpc is one I know of). But the other problem you will run into is getting all the parts for your laptop. As far as I understand your only source is ebay for this and even then your choices are rather slim. There's been people on these boards who tried to even make their own chassis but I didn't read those threads in full, so if you're interested search around.
Long story short, laptop building is not as enthusiast friendly as desktop building.