Customize Gnome Desktop and setup with Fedora

I intend to make my own linux distro by customising an existing OS. As per my research Fedora / Ubuntu is the best OS for customising desktop environment. I want either of their's desktop environment (gnome) to be customised as per my requirements. Most probably it would be gnome extension. I love the gnome look of fedora the most but yet I want to customise it at some points. Most of them would be layout related changes. Kindly share me your portfolio or past work. Thanks.