I like to start my design documents with a solution section (sometimes including time breakdowns) - it's a good way to get non-technical audiences up to speed on what will happen, and allows the technical audience to frame their thoughts on the rest of the document.

They usually follow the structure:

1. Solution

2. Context (problem space)

3. Alternatives + Details

4. Logic behind the decision for the solution (reiterating drawbacks)

5. Time/task breakdown (if applicable)

6. Closing remarks

7. Notes (usually only useful for technical audiences engaged in the implementation)