I am an Architect, Design-Builder.

I just purchased a house that I'm interested in expanding and I need a architect.

Not so cheap, but the architect also works to get everything through the city, even non-design issues.

During the weekdays I am an architect within the commercial multi-family and office sectors.

You may want to consult with an architect who knows the area --- I may be able to refer you to someone. 

Did you have a licensed architect involved, or did the contractor just sketch some stuff and put it on construction plans?

I can't remember which BP podcast it was but one guy said if my tenants pay less on utilities they have more to spend on rent (my opinion is it would reduce turnover and vacancy but not necessarily command much higher rent).You mention a roof garden make sure your structural engineer is aware of everything you are putting up there the roof may not be designed for much soil and pavers.If you have radiators I think this thing is genius https://www.radiatorlabs.com/our-system/how-it-wor...I would look at getting spray foam insulation into the wall cavity but consult with a good architect or building envelope designer to specify it because if not done correctly you can get mold inside your walls. 

When I first started out I thought I could build a lot more units before I hired an architect on board actually and per what @Brent Coombs referred to, if you build you might spend 1-2 years in plan check and approval, and another 1-2 years, possibly longer to build it out.

You need to hire a civil engineer and an architect.

I should also note for more complex renovations an architect and engineer would be involved in the plan creation process.