Properly executed cladding should not cause any issues, but I have personally seen first hand that badly installed cladding literally destroyed a building structurally by creating a great environment for fungus to spread. Before making your decision you might want to go over this official guide on cladding: http://www.fema.gov/media-library-data/20130726-1707-25045-0913/chapter9.pdf It gives a lot of information on how cladding works, behaviour of water on cladding etc. I would personally never use cladding, but I have seen cladded buildings doing absolutely fine for 25+ years. Saying that they were in mild climates with no coastal winds or airborne salt. I'm not an expert on cladding or coastal properties. Insulation on an old house is always a good idea, as it really helps with cold spots and can greatly reduce fuel bills. With smooth render, you can also add additives to it to help inhibit salt, which would increase its lifespan in your area.

Hey Saml1992, We did get the bradstone rendered, we went for K-Rend all over, including covering the existing render on the extension - and we couldnt be happier with the finish. We also decided to combine it with cement board cladding and it all came up a treat. I just took this photo (apologies its a bit gloomy here) so you can compare it to what it used to look like! The render and cement board has been up for 14 months now. (Still not finished the front steps though!)

This frontage is 6 section each section measures 3 metres the height of the building is 12 meter. I am wondering what would be the best design as the building is zigzag shaped.

Has the work already been carried out? Certificate of lawfulness suggests so. If this is a planning application then the planners should be able to advise on what might be acceptable changes. Is there an appeals process? Might be worth engaging a planning consultant who can advise. Planning departments can vary considerably in how they apply the rules, some areas are fairly flexible, others less so. If you’re in a strict area a landing consultant who knows how that area operates would be worth considering. Also, changing the roof may not be compliant if the new roof is vastly different to the original.