Anyone made their own linux distro?

Look at that image. Each of these distributions has thousands of people actively working on it. But they're not actually developing software: they just package and distribute the same exact software in slightly different operating systems which are just different enough to be incompatible but not different enough to be distinct from a technical standpoint. Think about how many man-hours have been wasted because Linux people think that this kind of duplication of effort is necessary.

What GNU/Linux sorely needs is some integration. It should be developed like the BSDs are, as a "base system" to install additional software on top of.

Remember what Rob Pike said: "Microsoft succeeds not because it’s good, but because there’s only one of them."

The base system is GNU

Maybe the duplication isn't necessary, but the current distros simply SUCK. That's why I wanted to make my own. They install too much shit by default, and don't even bother to configure those programs properly. Salix comes the closest (so I use it) but it has some flaws. What I wanted to do was to modify Salix to include some software that I think it lacks, and replace some software with what I think is better.

Just write a gentoo installation script.
If you want more control, or a different package manager / basic tools, write a lfs script.

Is not a script the best way to build what you need?

...

That's not how BSD works. *BSD (OpenBSD, FreeBSD, NetBSD) systems are not at all interchangeable.

It has a kernel, the kernel is the Linux (well, Linux-libre) kernel

Make a custom Debian distribution. I think they call them 'blends' now. You can reuse a lot of their security support and maintenance that way. For packages you need to change rather than just select, you can set up similar project infrastructure to Debian's. I use reprepro to maintain a handful of customized packages for my company's firmware, and use a custom kernel that is just patches against Debian's. Be warned that customized Debian kernels for single targets require some degree of autism to manage.
All the goo required for how you want your distro to run is available, like liveCD support, but I find it easier to just write the initramfs scripts myself as it's only like 20 lines vs an ocean of config settings. I strongly recommend extlinux over grub if you're just on x86 as it avoids the nightmare of getting grub to find boot when the drives names might differ.

it's going to be
systemd-apt or systemd-packaged or something stupid.

Linux is a kernel.