I might contact the actual owner and coordinate with them as well since they have may an completely different story and may be able to provide help and insight to you as well. 

Next time I'll start with the engineer.  

No, DIY is not the same as a virtual site visit or a study done by engineers @Dana YobstAs @V.G Jason said, you could very likely cost yourself more in time and money.

You may have to search a bit for the right contractor or engineer - sometimes I see one solution dominating in an area - "that is how we always do it" 

Whether that is most contractors, hiring an engineer, or getting self-educated.

These methods include: Detailed Engineering Cost ApproachDetailed Engineering Cost Estimate ApproachSurvey or Letter ApproachResidual Estimation ApproachSampling or Modeling ApproachExperience or “Rule of Thumb” ApproachIt’s important to understand the differences between the approaches including which one best fits your property and the reliability of each approach.DETAILED ENGINEERING COST APPROACHThis approach compiles the costs from construction and accounting reports to build a report.

@Phil SheltonYou would need a civil engineer to provide a drawing to get submitted to zoning and get a permit if it passes zoning is most common This also depends on the road - if it’s a state road forget it as it will take a year to get approved and cost a fortune - if it’s a local road process not as cumbersome but don’t expect this to happen quicklyIn some instances you may have to prepare sight distances etc to make sure it’s safe to add a curb cut

Quote from @Jeremy Dugan: I am a US Air Force and Massachusetts Air National Guard veteran with 20-years of experience as a military Civil Engineer.

Work with your attorney for what is needed to insure all subcontractors get paid by the General Contractor.Make sure the insurance covers Construction period and also materials.Talk with your Commerical insurance agent and they should address the above questions with you.If this is an older facility make sure your engineering firm has covered Fire Suppression systems and any Storm pond or drainage systems. 

@Anade DavisHi Anade, You’re on the right track with reaching out to your survey and engineering company—they often have strong connections to local contractors.