Basically, GNU / Linux Distro is the core and "package of packages" (GNU packages) of one choice. People create distributions to perform certain tasks, such as a server, desktop distributions, multimedia oriented distributions, etc.
Building a linux distribution can be a really educational task, as you can learn how to build a Linux system from scratch.
I recommend you cheking LFS (Linux From Scratch) . His project, which will help you build your own linux distribution from scratch, and believe me, this is great fun, and indeed, YOU WILL GET MUCH. If you are interested in learning how the linux distribution works, do not miss this. The web page says:
Many people wonder why they should sort out the problems of building a Linux system from scratch, when they can simply download an existing Linux distribution. However, there are several advantages to building LFS. Consider the following:
LFS teaches people how Linux works domestically Building LFS teaches you everything that makes Linux tick, how everything works together and depends on each other. And most importantly, how to tune it to your own tastes and needs.
Building LFS creates a very compact Linux system. When you install regular distribution, you often end up installing many programs that you are likely to never use. They just sit there, taking (precious) disk space. It is not difficult to install an LFS system of less than 100 MB. Does that sound so much? Some of us have been working on a very small embedded LFS system. We installed a system that was enough to run the Apache web server; total disk space usage was about 8 MB. With further withdrawal, which can up to 5 MB or less. Try this with regular distribution.
LFS is extremely flexible. Building an LFS can be compared to a finished house. LFS will give you the skeleton of the house, but this is for you to install plumbing, electrical outlets, kitchens, bathrooms, wallpapers, etc. You have the opportunity to turn it into any type of system, you need it to be fully configured for you.
LFS offers added security. You compile the entire system from source, which allows you to check everything if you want to do this and apply all the security fixes that you want or need to apply. You do not need to wait until someone else provides a new binary package that (hopefully) fixes a security hole. Often you never know whether the security hole is fixed or not unless you do it yourself.
Of course, there are other tools for creating a linux distribution based on your HD installation, possibly for backup.
And many other scripts to get you started, just google for them. Of course, they all look like user-oriented automated tools, so don't expect to learn much from them.
There are many, thousands of Linux distributions, so obviously it is a waste of time to try and create the “perfect” Linux distribution and compile it using ubuntu, mint, etc.
I still recommend that you check out Linux From Scratch, as well as the weekend educational project. Believe me, you will learn a lot.
It also covers the built-in linux distribution for building ARM processors, etc.
If you are in an embedded world, the Yocto Project is worth a look.