question

You're not actually passing in the model background. The model background isn't in the Tools folder (that's just a node that points at the background) it's in the model:

So your code should just be:

switch_hideshape (Model.find ("Floor Layout"), 1); 

Or if you wanted to turn off all the model backgrounds you could use those pointers to find them:

treenode backgrounds = Model.find("Tools/ModelBackgrounds");
for (int i = 1; i <= backgrounds.subnodes.length; i++) {
    treenode pointer = backgrounds.subnodes[i];
    treenode bg = ownerobject(pointer.value);
    switch_hideshape(bg, 1);
}