I've had lot's of drafting
In high school we had drafting classes where we drew up plans for houses. Each set of drawings had a floor plan, front rear and side elevations drawn to scale. From those plane a good rough carpenter could lay out the walls and build the house.
I would look for the same thing in a set of project plans, a top view, side views and front and rear views drawn to scale. The scale is important and would be a common one like 1" = 1 foot or 1/2" = 1 foot. This allows you to measure the drawings and convert them to actual full size dimensions.
Joinery details are also just as important, so exploded views of how parts fit together would be a great asset. The dimensions of the parts would also be needed.... depth of mortises, etc.
We also drew in 3 D perspective to better illustrate the overall look of the home, and this case the project. This is a pretty exacting artistic skill and not everyone would be proficient at it. In that case a 3 D computer modeling program is far and away your best bet. Sketch Up would be able to perform all the drawings and a perspective view easily.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)