Hi,
If you are a sole trader in the UK and you provide design services to a company based overseas then these services would be outside the scope of VAT.
You would therefore not be required to register for VAT although you could register on a voluntary basis.
You can see the guidance below,specifically section 2.9.
Who should register for VAT (VAT Notice 700/1)
If you choose to register for VAT then there will be an option to register on the basis of making supplies overseas.
The only basis on which there would be a requirement to register for VAT would be if the design services are related to a specific property in the UK and the registration threshold of £85K is breached.
Please see the guidance below:
Land related services
Thank you.