My Protrude works on perfectly rectangular fae only, so that may be limiting. It is here:

http://sketchuptips.blogspot.com/2007/10/plugin-protrude.html

Thomas also added a face division tool to his Edge Tools:

http://forums.sketchucation.com/viewtopic.php?f=323&t=24593&hilit=plugin

@bjanzen said:

Adjusting the grid opacity is a regression bug. I just tried it in 2.0 and it worked, but LayOut doesn't respect grid line opacity settings in 2.1. Ouch. Sorry.

b

Sorry, I didn't tell you before... I did the grid (because the spacing is not really the same between x and y) using LO lines and setting their opacity to 10 (the color is black).
I discovered a bug accidently 😄
But however, as I wrote in the first post, exporting my work in jpg the resulting images are exactly what I want them to be (and the same as I see in my monitor, that's ok).
I was just wondering how PDF has not the same output image as jpg. That was all.
BTW many thanks for your helpfull advices!