First step with any structural building project is to get a designer on board. Architect, building designer or a good draftsman. They'll know local legislation, construction processes, design as well as budgets and construction costs to name but a few. Remember though architects do more than just design and draftsman do more than just draw plans. You'll need to decide what you want the designer to do for you and choose the one that is suited to your requirements. Have a quick chat with them all and decide from there.

I'd be going back to the architect/designer and asking why the vent wasn't on the plans then armed with that info, I'd be asking your Turkey of a Supervisor why if it wasn't on the plans he didn't flag and insist on being given the EXACT code that he's referencing (including the details so that you can review yourself) as last time you checked YOU WERE THE CLIENT - It's a shame you've had this happen - your home looks as though it will be stunning, but others have said it wont be so noticeable when the building is done completely. The placement kind of makes sense since heat rises so you'd want it to be as close to the highest point for maximum effectiveness but you should have been aware. Check on the builders itemized estimate to make sure that you didn't miss it by accident so that if you did accidentally miss that one line item on a list of a million you able to prepare your argument accordingly.

Look at bigreaders photo -- I personally think the 'clean' tiles look great -- the colorbond not so great . BUT what you also note is that the part facing the street appears to all be tiled . A good roofer will keep the newer tiles out of sight -- you may even be able to get 'speckled' tiles that make it less obvious , or even get an airbrush artist or even enthusiastic art students to add a bit of charcoal and dark green on them . The white window frames and white gutters , in fact your whole house , looks 'clean' -- the tiles have some character , but even 100% new tiles wont look too out of place IMO , and changing to a shale or similar colouring would emphasis that your place is looked after IMO .

take your photos to the local tradies' hardware store (usually the smaller store with all the utes out the front) and ask for the best product to clean the discolouration and replace all the screws with new tech screws with the bigger rubber washers but, if it was my roof i would take the opportunity to lift the roofing sheets and check for any damage to roof structure clarify the source of the leak (often not directly above the inside drip) check all along the flashings and trims (consider new insulation to suit your local climate) and then replace all the screws