Models, covering costs and HMRC

[Papillion]

I'm sure I've seen this question before but have done a few searches and can't find it, so sorry for repeating.

If one was to advertise for models and charge a fee to cover cost of materials does HMRC still need to be informed for tax purposes?

I am off on a free self employment/HMRC course next month but would love to know the answer to this one now.

Thank you x