I think you are taking the wrong approach here. If you can write such a document, it would be extremely valuable to the whole community but havn't you wondered why such a document doesn't exist already??
It's because it will take you forever to formulate. Unless you designers have designed for SharePoint many times before, they're likely to design something that will be hard to build.
Ideally you would hire a specialist supplier (like who I work for) to do the designs for you and yo simply implement them...
Or you sit with your designer and show them what is or isn't possible in SharePoint UI. This will be an iterative process but you will learn something. Perhaps you start playing will the out of the box CSS and see what each style changes.
Either way, SharePoint UI design should be dictated by someone with SharePoint experience and this is what's most likely to save you pain.