Also what type of cladding would anyone suggest?

10% is actually the rule of thumb number that I have heard used for years. Of that 10%, about 60% typically goes to construction docs and the other 40 goes to the earlier phases of the job. Pre-design, if any, is often done hourly. None of this is set in stone anywhere and it will vary depending on the designer's experience and overhead, the complexity and size of the job, etc. There is certainly nothing alarming or unreasonable about asking 10%, and in design, as in most things, you generally get what you pay for.

When installing over top of old ceramic/porcelain be aware that you will most likely have to "sink" the old tiles in cement to do this. That means grinding down the tiles a little (rough up the surface) then the self leveling cement is poured and allowed to dry. The new floor is then laid over top. Vinyl is notorious for requiring EXTREMELY flat surface. A ceramic tile rarely has this requirement (grout lines and "high spots" around tile corners give problems). A glue in place tile is also going to have the same problems and the same solution = sinking the tiles in cement. This adds extra costs to the floor. A rigid floor like a cork floating floor can handle a bit more floor deflection than vinyl or laminate planks. If labour in your area is relatively cheap...you could probably have the tile removed and the sanding of the mortar done for the same price as coating in concrete. You will also have the luxury of being able to lay any floor you want once it is done AND you don't have to worry about increasing the floor height. It is possible to sink the ceramic in cement...but is it the most cost effective option? Maybe not.

I didn't see this either , and how long is a piece of string ? Wellington ( a bit like parts of Queenstown ) is known for steep slopes and high winds , so the actual design will affect things a lot -- my sister once 'conned' me into moving her to Wellington when she got a Government job . We loaded one of my small trucks and drove several hours , when we got to her new place on the side of Mt Victoria with lovely harbour views , it seems she had forgotten to mention that the new house was the one up there -- yes , a 1920's build 130 steps up from the street . Hard enough moving a glass fronted china cabinet and solid Kauri 1880s dining table -- imagine carting every bit of timber , tile , window , kitchen appliance up there !