Well, by using it carefully and possibly sculpting it a tiny bit when it's still wet, you might be able to get it to look that way, after letting it cure and then painting it.
The problem with great stuff is that you have to use it in stages - it is a foam, so if you pile up too much "uncured" foam, it will fall over.
I just got done using it to make a form of sorts while rebuilding my kitchen (needed to add concrete under a section and great stuff was the easiest way to make a small 'wall' to pour concrete into. I had to spray some, wait until that hardened, then spray a little more on top to make the 'wall' taller, wait, spray, wait. It cures fully in 24 hours.
But beware - as soon as you begin using a can, you need to use ALL OF IT within that day, probably within 8 hours, because any foam left in the dispenser tube will harden there (it warns of this right on the label). No way to clean out the dispenser tube, either, because it's a nasty chemical. Make sure you wear gloves - any that gets on skin is like super glue.
It might take you a few cans worth for practice to get the type of texture you want, but quite a few people do make their own enclosure furniture and wall decorations out of it. It definitely needs to be painted or otherwise coated before use, to prevent water or humidity from causing it to eventually crumble, though it is pretty sturdy once cured.
Good luck!
-----
Lauren Madar - OphidiaGems.com | CageMakers
1.0 Ball Python, 1.0 Hog Island Boa (RIP DeeDee), 1.1 Hypo BCI, 1.1 Surinam BCC, 0.1 Green Tree Python