Please recommend a good technical design tool for iPad or OS X I'm looking for a tool that will allow me to create isometric and flattened designs. I'm looking for an application that allows designing of engineering projects for wood working.

I've spent a lot of money looking for an app but most are tools for sketching and artwork orientated.

Some features I'm really looking for are:


Easy to use
Isometric and flat views for same design to be shown
Vector based design, allowing me to resize, move objects individually
Measurement and scale support, allowing me to specify a scale and then size elements based on that scale (in metric notation)
Layers support would be preferred to allow measurements to be supplied on a separate layer


I don't want an overly complex tool, I just want a nice tool to do the job of creating designs alleviating the need for me to use pencil and paper.
If you haven't already, check out Google Sketchup. I don't think its on iOS yet, but it is lovely in its simplicity, short learning curve and flexibility. There are tons of YouTube clips showing off features and tutorials.