I would like to build my own gaming computer for £300 excluding the OS, Monitor, Mouse and keyboard. How much should i be spending on each part
You can't really build a gaming computer for £300, to be honest.
What resolution are you wanting to play at, and what games will you be playing?
Mainly Minecraft, skateboarding and other action sports games games, a few shooters like tf2. I don't expect it to be amazing, but just enough to run them smoothly.
And the £300 won't include a monitor, keyboard, mouse, case or operating system,