I know this got out of hand on MySpace and I don't think I've seen it on Facebook. Do they provide any way to do this?
Facebook does not directly provide a service to customize your layout; but there are some 3rd party services / plugins on the net to provide Facebook layouts to your profile. I have never tried them but Naevius is one of them.
A search for "facebook layouts" using your favourite search engine should turn up some more.
The option for Facebook layouts is through a third party app or plugin on the web. I've tried FaceTheme and Webfetti but had issues so I decided to uninstall. I am now using PageRage and I am finding that it works quite well. They also give you the option to create your own layouts.
Not really customizing the layout, but a useful Chrome extension for hiding those annoying adverts https://chrome.google.com/extensions/detail/cbpaedifajkadcemkafopbniflgiimkd
You can customize how Facebook's layout is presented to you in your own browser, for instance if you have been switched to the new Facebook design that they are currently rolling out, but want to go back to the old design, you can do so either by using the Facebook provided switch to "go back to classic mode" or if they have taken that option away from you, you can use a simple browser extension to get the old design back
There are a couple of choices that i have tried and both work really well.
Revert Site: https://revertsite.com This is a very simple and easy to use extension that lets you switch your facebook layout back to the old style one.
FB Purity: https://fbpurity.com This is a more advanced and feature packed extension with lots of Facebook customisation capabilities, including the ability to filter out posts containing words or phrases you are not interested in, hide all the ads, filter out pictures of babies or cats or dogs etc
Of course part of the new Facebook design is a new option to switch to "Dark Mode", so thats another thing you can do to customise your Facebook layout, but of course it only affects what you see when you login to Facebook, other people wont see your Facebook profile in dark mode, just because you switched your account to "Dark Mode"
So there is a fair amount of customisation you can do in your own browser to change what you see, but if you meant you want to change what others see when they visit your profile then I guess the only customisation you can really do there is to change your Profile Image and Cover image.