SDL Education offers a Functional Design class that how to document schemas and templates, but also the prerequisite page types and content types.
Schemas and templates are not enough for a "CMS Design," you'll want to include:
- Who and Where: Organization including folders, structure groups, and the especially the BluePrint model.
- What: Content Model or the relationship between page types, content types, and to an extent, fields. These are typically based on wireframes and/or mock-ups but I sometimes see them missing from organizations that have done implementations without guidance.
- How: The Tridion-specific details including, but not limited to, schemas and templates.
No special format required for these, though you should call out things like global use and naming conventions. See a typical schema definition in table format on the PowerTools wiki, though I've seen indented formats work as well.
An actual document "template" would be part of a professional services engagement with SDL, partner, or independent consultant.
Architectural diagrams aren't much different than how you'd document Web and Application servers. It's good you're considering both types:
- Logical diagrams highlight the tiers and relationships between them. You might have boxes (or Visio server diagrams) for, but not limited to, "Content Management," "Publishing," and "Delivery," for example. Arrows show the relationships. Refer to some of Julian Wraith's whiteboarding recordings for the basics (relationships are more important than the diagram's look-and-feel). :-)
- A physical diagrams detail the specifics server quantities and what may be physical versus virtual.
You'll probably want to capture differences between DTAP environments as well. Your baseline documentation will be important for future changes, upgrade scans/audits, and troubleshooting.
Most importantly, a proper diagram can clarify confusion between Content Management and Content Delivery, which seems to be the biggest hurdle I've seen for those new to Tridion (or maybe this type of content management in general).