If 'Formalising the receit' (receipt) means 'recording' donations, then this will be done as part of your overall Shed financial accounting. Probably no need to issue a receipt for each donation, but of course an 'thank you' in whatever form is a 'must' which will help to build longer term support.
Public sector and other funders being asked to support projects/activities like to see diversity of income and donations (individual) and otherwise shown in your accounts will form an important part of your income stream, showing how widely you're supported etc.
Those Sheds registered as charities will know of the value added to donations via Gift Aid - i.e. turning every pound donated into £1.25 thanks to HMRC. Guidance on the HMRC website includes what record keeping is required
https://www.gov.uk/claim-gift-aid/overview