Hi guys !
I’m quite stuck with slab issue. I’m working on a plan, from an existing build. The slab is sloping (-2,5%).
No problem to rotate the slab, but walls are not joined on the slab like this :
The question is, how to have a slope and my walls follow this slope ?
I tried to answer with a simple draw, rotate the slab, but not possible to draw out the red or green axes.
Not telling me to rotate all parts of my model 
If someone has the answer, please tell me.
Thanks in advance 
No problem FCTM you are in Sketchup so you can do as you see fit.
It is unusual for walls to follow a slope, especially brick walls.
However, in this case, you can triple-click the wall and use the push-pull or move tool to align your walls with the slab.
TIP you may need to go to the edit menu and select “view hidden geometry” just so you can select an edge or individual face.
If it is a framed wall I’d recommend using the beam tool for the framework. Here are the tutorials: https://www.youtube.com/playlist?list=PLNRcN-A1tOEz0aOQliJS_iCaEY1e8S_Ml
Are you just drawing for estimating or are you drawing to submit council approval?
If you are drawing to estimate and you are using PlusDesignBuild I’d recommend drawing the sloping geometry using the Sketchup tools and then simply using the custom estimation tool to quantify and organise the BOQ.
Here are the tutorials for the Custom estimating tool https://www.youtube.com/watch?v=2q3deItEDDk
I hope it helps.