If you have access to YouTube, you can watch the video at THIS LINK
This video will show you how to extrude the 2D floor plan to a 3D house. The house the instructor builds is much smaller than the houses in the plans you have been provided. Make sure you pay attention so that you can transfer the concepts to your own model.
Extruding external and internal walls
Inserting doors and windows
Fitting a pitched roof
Adding textures/materials to your model
Interior design/inserting appliances and furniture
Tip for success:
Do not watch the whole video and attempt to learn all of the information in one go. Watch each chapter and copy what the instructor does in your own model.
How to create a hip roof in SketchUp.