To export the object, go to 'File -> Export -> 3D Model,' and choose 'Collada (DAE)' as the export format from the drop-down menu. To measure an edge, use the pencil tool, find the midpoint and stretch it out to the other edge midpoint, and note the measurement in the bottom right-hand corner. Make the model in Sketchup, and when you are finished pay close attention to the size so you can check it later. This is great if you have a Makerbot 3D printer and makes you produce models in a useful scale. This helpfully superimposes a box the size of the working area of a Makerbot 3D printer. To make your 3D model, open Sketchup and use a useful template like the one for 3D printing.
