Building a 64-bit kernel starts by getting the source from someplace like kernel.org, the source is the same for all supported architectures.
You might find the kernel-rebuild guide to be helpful in accomplishing the kernel building;
By reading both the kernel-rebuild guide and the documentation found in the extacted kernel source you should be able to tune the kernel to your hardware. It may take a few tries to build a working kernel tuned for your system, but that's part of the learning process.
Start by installing a distro of your choice, most provide x86_84 installation media.