Where to start with extension?

[Babyreindeer24]

Evening
Apologies for sounding clueless but I am!

We're in a position to look to extend our house with an extra room and bathroom. Where do we start? Quotes? Planning permission?!

Thank you

Designs - so you know what you want

Quotes - so you know how much it costs and who to go with

Planning permission - so you can put the designs forward for approval and your chosen builder / architect can amend if needed.

That’s how we did it anyway!