As an archViz, I use Sketchup all the time, and I Have created a very personal workflow. Let's just say I wouldn't be so quick in modeling without a number of plugins.
The plugins I use the most are:
Extrusion Tools
Tools on surface
Opener (also referred to as HOLE)
Lattice-izer
Instances (so I can select all the instances of a component in 2 clicks)
round corner
joint push pull
fredo scale
mirror selection
Rot90
I also make vast use of the sandbox tools, and I have a personal set of keyboard shortcuts. Section cuts I use a lot too.
To make roofs with tiles and everything you could use: IstantRoof
http://sketchupdate.blogspot.com/2010/11/instant-roof-instant-productivity.html
wich comes in two versions: free and pro.
Hope this helps π