My main goal was to have the towers look twisted & rickety - as if it only exists by the help of magic. So I started by cutting squares of insulation foam and poke a bamboo skewer through the middle. After I stacked enough squares to the desired height, I spun each layer slightly further than the piece below it and glued it into place.
Using a hotwire cutter, I followed the flat faces of the squares around the tower to cut off the uneven edges.
I repeated the process with wider squares so I that I had main larger tower & a secondary, skinny tower. I cut chunks of more insulation foam to wrap the bottom of each tower with cliff-type rocks. Other details were added right away like the doors, and cliff ledges to be a landing for the doors & bridges.
I tend to be a glutton for punishment when it comes to detailing terrain. For the brick work, I took my hot wire cutter & scarps of foam and cut bricks of all different sizes, thicknesses, etc and glued each one on individually. Doors & windows were framed first, and then the remaining wall was filled in.
I had originally intended on filling in the gaps between the stones with some sort of grout, but it looked fine without it. (One thing that was an issue was getting the paint in between the bricks all the way to the core of the tower. The second time I built towers like this, I painted the flat core black FIRST and then started gluing on the bricks. That helped a ton.)
As far as the painting process goes, I started with a black base coat on everything. Then using a sponge, dabbed on a medium gray coat on the face of the bricks. I took the sponge again and did the same with white. You can see the difference in the picture to the left. The wall on the left is at the gray stage; the wall on the right has the white added.
I decided the only way I was going to get the roof to curve the way I wanted it to was to use clay as my base structure, but I didn't want to waste a bunch of clay or make the roofs too heavy. I started with cutting 4 triangles out of cereal box cardboard and taping them together in a pyramid shape. This will keep the inside of my roofs hollow. I prefer to use oven bake clay, so I didn't want this part to catch fire in the oven. I wrapped it in aluminum foil so that after I apply the clay I could remove it before baking.
I took my clay and smoothed on a thin layer over all four sides. (Never mind the swirling color. I had mixed scraps of yellow & black together to get rid of some excess clay I had in my inventory.) At the peak, I rolled out a tapered rod of clay and smoothed it down over the top to meet the 4 sides. I gently curved the rod around to act like a drooping peak to the roof. Once the shape was complete, I peeled the tin foil off of the cardboard structure and place the roof into the oven for the recommended time. After it was cooked and cooled, I peeled the foil from the inside of the clay.
To add the shingles, I cut small square/rectangles from cereal cardboard. The using super glue and working in rows starting at the bottom, I attached each shingle individually. The corners were covered with larger rectangles folded in half. The peak can get tricky since it is round and the tiles are flat. Putting a slight curve into your cardboard before gluing it on will help it look smoother and give your glue a greater amount of surface contact area. To finish off the peak, I cut a "Pacman" shaped piece of cardboard and pulled it together to act as a cone.
Steps were added to the front with a strip of clear plastic attached at an angle from the door and to the bottom of the base. Steps were made using more bricks attached to a piece of card board with a wedge underneath.
The wedges are what I glued to the plastic, so even though my plastic is at a slope, each stair appears to be floating flat.
To create another floating walkway between the two buildings, I cut another piece of clear plastic and attached stones to it. I also added a rare earth magnet on each end. Under each platform by the door, I cut a slot and added a regular flat craft magnet to hold the path. Using 2 rare earth magnets made the bridge hard to remove and 2 regular craft magnets were not strong enough, but mixing them made a fairly strong bond that could still be removed without doing damage.
To give everything a wintery feel, I mixed together basking soda and white PVA glue. (Make sure to use a good brand names, otherwise your snow may yellow as it dries.) The ratio is definitely something to practice before adding it to your piece. If your mixture is too dry, it will not stick. If it is too wet, it will drip all over and look like cake frosting.
I also made some icicles by using my hot glue gun to create streaks on a metal container. Once cooled, I could peel them off and then use another dap of hot glue to attach them to the building.