There are structural concerns, and legal concerns that need to be addressed to properly develop an inspection letter.
General Things to include:
Date of Observation
Duration of Observation
Weather during observation
Name and Title of Observer
Depiction or description of each area observed including pictures
Statement asserting whether each item observed was or was not in general conformance with the contract construction documents
More specific:
Shear - Sheathing selection, nail selection, nail placement
Roof Diaph - same as shear , check chords
Nailing - nail selection and placement. Installation method could be noted.
Holddowns - installation per manufacturer recommendations? Correct placement? Correct anchor rod selected.
Hardware - installation per manufacturer recommendations? Correct placement?
More more specific:
Any particular or odd conditions that are detailed in the construction drawings that were observed for conformance.
Any limitations, were certain areas unable to be inspected?
As far as legal goes, be careful with language accepting or approving anything. I try to use the term 'In general conformance'. There is more to consider here may want to prepare a sample letter and go through it with a lawyer who is experienced in the field of structural engineering.