Not a good idea unless your BMI is under 12, tall steps and a long handled broom is far safer, or use one of those sponge and squeegee contraptions that are also good for the windscreen.
Hi Dave - It's normally safe on the flat area to the rear of the overcab, but there is a weight limit. I had a look at the on-line handbook, but couldn't find any reference. If you post your question on the www.swift-talk.co.uk forum (free to join) Swift are usually prompt with responces. However a word of caution, almost all motorhome roofs can be very slippery when wet.
Thank you for your thoughts, looks like I may have to ask the grandchidren to do it for me , lol
will check out the forum at swift link yiu gave me, thank you