I've done a few dual Phase I/PCA/PML projects and can only say that without an engineering/architecture background, it will be a bit of a challenge. 

Often times when there's an ESA, there's a PCA or PCA/PML (Probable Maximum Loss = earthquake/retrofit risk) counter-part.  It involves inspection of all aspects of the building structure for the purpose of determining projected maintenance costs, and set-aside dollar amount (deferred maintenance).  You basically have to look at many of the same things that you would take notice of during a Phase I site walk, such as interior and exterior building materials, drains, etc., but you also have to pay much more attention to things such as piping, plumbing systems, fire suppression systems, mechanical equipment, servicing schedules, and systems, ingress, egress, curbatures, paving, lighting systems, roofing system, landscaping, etc.

Hopefully you will have someone available to help you with the costing and PML calculations.  Expect to be there on-site much longer too!