With Google Maps, you can do amazing and helpful things including creation of detailed engineering planning. Check this out from GMapsMania

Roof Mapper is a Google Maps based tool that was developed for a roof engineer who needed a way to create detailed plans of buildings' roofs, in order to display where work needed to be carried out. However I'm sure the tool could be really useful in other contexts where plans need to be created for a specific area.

The application allows the user to select any area on Google Maps and then draw a polygon on top of the satellite view. For example, tracing the outline of a roof on a building.

After the roof's outline has been traced on the map the polygon area is then displayed on a gridded area beneath the map, which can then be printed out to use as a plan for what ever work needs to be completed.