Quote - ...if i use them for the final image, with all the tiles on the roof i think the rendering takes lots of time...

Yeah, that's what I meant about the computationally expensive warning; and also some of the comments I made in that PM I sent to you.
The overall quality level (and especially the quality of lighting) in a Kerkythea render is very high. There is always the trade off of quality to render time in CG. No way around it. It's simply: # of calculations divided calculations/second.
Some engines are more efficient; but it's never a huge difference; quality settings being equal.  A quicker engine will make worse renders, but a lot of times max. quality isn't needed. Kerkythea doesn't have much in the way of making low quality renders, like most of the 'speed renderers' do.

I'll look around, see if I can find some other quicker render engines that you could use for your Sketch Up models too.

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I haven't given up on working on this idea here in the thread. I'm just going through a motovational dearth right now w/ CG.

Friends don't let friends use booleans.