Gaming desktops:
You can build your own gaming desktop using PCPartPicker -
https://pcpartpicker.com/ from looking at ready built models and making your own. Almost any computer component can be ordered from
https://www.amazon.com/PC-Parts-Components/b/ref=nav_shopall_components?ie=UTF8&tag=basebal-20&node=193870011
Visit
https://www.reddit.com/r/buildapc for ready made builds & technical help
Gaming laptops:
Gaming laptops are hard to upgrade since most hardware components (except RAM) are hard or nearly impossible to upgrade
It's buy once, use it policy for gaming laptops. If portability is want you need, then go with gaming laptop, else desktop is better option
In gaming desktop, you can easily upgrade almost any components in the future. But, that's not possible in laptop (as you'll need lots of techincal knowledge to upgrade component in laptop). Only RAM, screen, keyboard, touchpad, etc can easily be upgraded in laptop