You will need a lot of time. Take a dedicated partition and follow the LFS book.
To save some time you can use the ALFS-script (automated LFS).

Really nice and interesting approach to Linux, you need to take a lot of time for it, process is tedious but after all you'll have your own personal running system, it takes ages if you'd like to customize different machines, you can do it on your personal computer if you've a lot of spare time. I've spent so many hours on LFS, really powerful but even time consuming, later on I've switched to gentoo, not so powerful like LFS but still really close to the source and the kernel itself.