Build a laptop? From the ground up? Well you have already encountered the first problem with that, you cant buy mobile cpu's or gpu's unless its from someone who ripped one out of an existing laptop and is selling it. They also don't sell laptop motherboards, so again you would need to find one and its shell since many laptop mobos are proprietary and wont fit in other laptops. Building a custom laptop is not something many people do, there is no market for it that i'm aware of, it's not like building a desktop.