Both your selections of HVAC templates make sense. PTACs aren’t usually installed on roofs and every room typically has its own PTAC hanging off the exterior wall.
Writing an OpenStudio measure is definitely one way to do your research but I know Ruby and the OpenStudiop SDK have a learning curve. If you have more knowledge of Grasshopper than you do Ruby, you can alternatively build a custom HVAC system component-by-component using IronBug and you can apply the HVAC system you create to your OpenStudio model like so: