Converting pen sketch of garden design into scaled CAD drawing

I am a garden designer based in the UK. I have designed a garden using pen and paper and would like you to produce an A3 scale CAD drawing that I can then present to the client.

What is your process? Can I send you an initial simple line drawing you then send back and we make some small alterations together to save me having to draw it out again.

I will also need to colourise it.

Look forward to your response.

Many thanks

Titus