I think the first step of the process is getting the land surveyed and speaking with an architect.  

Work with an Architect who will also pull permits along with drawings.

Network and build connections with architects, contractors, land surveyors and even other investors who may have a background. 

Reach out to a contractor for some numbers or better yet to an architect to have some preliminary plans drawn.Also keep in mind that material prices are currently very volatile and contractors most likely will not be locking in prices.

lmaoIF your Dad is "going to build a duplex" AND you still want to be involved in the RE industry... ask him to show you what he can or wants to... all he can: from the planning, budgeting/financing, scope of work, drafting of plans or hiring of a Designer/Architect, dealing with the city and Codes, the GC, subs (or if he lets the GC do it all), etc etc ...

This is the actual text from the email he sent me "Architect would take rough estimate about 6-9 month to put together .That included all building permits ,plans Architectural, rough plumbing, and electrical, and HVAC.Now that is a separate cost to you we don’t include this prices in out bid.Now to build you 3 units 850 sqft each one Bathroom and two rooms .With laundry room.closets and kitchens areas .No flooring , no lighting , no cabinets ,Just ONLY , your rough electrical , plumbing.

Start calling real estate agents, general contractors, sub contractors, property management companies, lenders, architects, designers, title companies, stagers, etc.

Hire architect that does the plans + permits, then hire a contractor to do the job, some contractors have already done a retail demising, so it would be easier for them. 

Most of what you see comes from my training and doing presentations as an Architect. 

Look up AIA (American Institute of Architects) scope of work.