Finally had a chance to work through the Piranesi tutorials, so here's the first result.
6-LWadsworth-SH-viewS-alt.jpg
A higher resolution version of the same image is available in this gallery on Picasa. (The faked "etching texture" of the background texture is more visible in the higher res version.)
I rather disliked the original view towards the South (north elevation in perspective) shown in the first post of this thread because of the non-human (but not particularly bird-like) point-of-view. This is more reasonable, from eye-height for a 6' tall human. Pity it's too late to re-submit the image.
I'm finding Piranesi to be a fight...so far, it seems to be the most expensive Photoshop accessory ever (as far as I am concerned), because almost inevitably the output needs pixel-scrubbing and layering in ways that don't seem easily achievable with Piranesi alone. I'm not sure I like this as much as the "bad photocopy" pre-Piranesi NPR renderings posted before, although it is in fact much more like a Schuiten-type illustration (which may not be a good thing--there's something deceitful about faking older illustration media with digital means. This is not a pen-and-ink drawing, anymore than a VRay rendering would be a photograph).