Architectural drawing is a natural application of computer-aided design. One possibility is creating the floor plans for a house or business. Other architectural drawing projects you could create in a CAD program include the elevations for a building or a schematic of the plumbing and electrical wiring plans. Another alternative is a landscaping plan, using shapes to represent trees, bushes, flower beds, paths and decorative highlights.
These projects are where CAD software really shines. Engineering and design projects can show a single component in great detail or an entire system of interlocking parts. They can range from rough representations that give a general idea to incredibly specific, technically accurate models of complex mechanisms. Ideas for this sort of project range from the simple, like drawing a screw or a set of silverware, to the complex, like a car engine or a microchip.
While it is generally used for technical applications, CAD software can create beautiful imagery and sometimes even animations. CAD-based art projects can include virtual sculpture, abstract imagery or representations of real-life scenes or objects. One idea is to compose fruits or household objects into a still-life and then attempt to re-create the still life through computer aided design. For a more difficult project, try creating a virtual bust of a person you know or from a photograph.
This sort of project would use the CAD program's capabilities in a relatively unusual way: creating flowcharts, mind maps or other abstract representations of a system, project or organization. The capacity to design in three dimensions allows a greater complexity and richness to the visual representation of systems. Projects in this category could also include things like family trees, with the third dimension used to link people to the places they lived or the jobs they held.