Buff/Hannaman,
thanks for the comments! For the "recessed" brickwork for the second pic, it's real easy. At first the whole building is just one flat surface. I then took a hobby knife, and carved out som jagged lines here and there. Then I took a 6mm wide flat edged hobby knife, and gouged out the area, about 1 or 2 mm deep. Kind of like carving a pumkin. I then started scribing the brick work. For me it's kind of a reverse process, alot of people think/ask the same thing about the buildings, wether or not I scibed all of the brick work, then added a skim coat overtop. When I tell them the process I just explained, they get that "oh crap, why didn't I think of that" look LOL
Gregory, I tried a method similar to what you described, but ended up in disastor. I've really simplified my method, and that's using the big lego blocks to make my form, then put a sheet of was paper over top of a piece of plywood, put the form on top and add my plaster mix. Gently rock back and forth to level everything out, and wait to cure. Once the form has been removed, I usually let cure for a week, as I add tile grout colourant to strengthen the plaster, and it takes a little longer to dry.
When fully cured, I sand all the edges, removng any of the little bumps that are caused by the spaces between the lego blocks. I'll then scrape/sand the top surface to remove any air bubbles and to level out the piece. I then draw what I want on the plaster and take my dremmel tool and carve out the shape. WEAR A MASK while doing this, it gets VERY DUSTY!!!! Then you can start doing brick work or what ever you want. I'm fortunate enough to have a big compound mitre saw with a big blade, so cutting and squaring off the piece is a cinch.
OH, don't throw away any of your cut offs, or for that matter, any left over plast from your initial pour. Save it, and take a hammer to it, and bag it to use for rubble. Hell, I'll just make up a sheet of coloured plaster just to make bags of rubble! Good luck!!
PS - no toothpics or wire to support the plaster, just mix, and pour!
"There you go with those negative waves again!"