A good Expediter is a start but you may need an architect also, if there are things the DOB deems necessary for legal 2-family status.

Do I need a architect for the technical drawings ?

I have been using mostly small time handymen and contractors for rehabs and we never really needed site plans, architect, drawings ect...But now we are rehabbing a 3 story 23K sq/ft building and I want to show the city and prospective tenants we are professionals.Who do I go to for site plans, floor plans - would it be a construction company or an architect ?  

One thing we do is we talk to a lot of architects and engineers, as they are on the front end of it.

@Michael Mahung you would want to consult with an architect ASAP.

Hi, I'm looking for a great architect that knows the zoning and regulations for DADU's in Nashville.

Jerryll nailed it with his thought process.I've done house flips where I knew the profit would only be ~$25k at the end of the day, but those houses just needed a quick and easy refresh before re-listing for sale just weeks after I bought the deal.Then on the other end of the spectrum I have deals I'm pursuing that have a best case scenario net profit of $1M+ which require a ~2 year build out an a team of world class architect and builder to pull off. 

But after you account for architect fees, design fees, engineering, and construction costs of $300/PSF+ you are going to end up spending more to build new, almost guaranteed.If you're new to real estate investing and construction, as others have suggested, you should find a house that is already built. 

The other option is to bring in a construction manager who can manage the architect and GC and they also could provide you a budget and manage the architect.

,My wife and I, both architects by day, are taking a deep dive into wholesaling and are aiming to start pursuing deals this July.