Hi, I have to make some assumptions here. Import the drawing into Sketchup. there should be some known dimensions within the drawing or use the drawn scale if it has one. Measure a known distance with the tape measure. My second assumption is that you will be using metric, I would suggest millimeters, so you would import the imperial plan drawing into a metric mm template. Now scale the drawing by selecting the drawing using the 's' shortcut on your keyboard. scale by moving one of the diagonal corner points (which is uniform scale) you can either play around with the scale until you finally get your known imperial measurement and measure it so it reads in millimeters the correct conversion to millimeters. Or you can calculate the scale on your calculator and type in the scale factor directly.

So now the short version:
So forget about the 1:40 thing altogether. Say you can find some measurement in the drawing that is 10 foot then scale it so that 10 ftmeasurement reads with the tape measure as 3048mm then you have done your job and you can build from the plan without having to measure anything.

If you are drawing in imperial then simply scale the underlay drawing in an imperial drawing template till the tape measure reads correctly i.e. 10ft reads as 10ft
Cheers

Thanks guys, as it worked out I did not have a face ready for the texture......one of those Duh! moments

I am at a loss to understand why when navigating in Sketchup you are suddenly navigating trough heavy mud with the mouse and getting muscle burn with the ineffectual center wheel but as I grab my 3d Dexion "mouse" with my left hand the mud is gone and easy navigation returns. Surely this is an issue with the mouse/SKP navigation if the issue disappears with another navigation interface Surely this can be fixed in 2016