First step - acquire plaster. I found the biggest, cheapest tub of plaster I could find at the Hobby Lobby & it cost me a whopping $3. Using the Hirst mold #52 and their plaster mixing instructions, I started casting my blocks.
I started my construction upside-down in order to make sure the top floor was all level.
The Hirst blocks do a really good job of fitting together, but there are a lot of seams around the windows. Too many for my taste...
... so I dabbed some spackle with a tooth pick into some of the gaps to connect the bricks where appropriate.
After the height of the tower was built, I flipped it back right-side-up to add the last 2 rows for the wall & the crenulations.
One thing the molds does not account for is a door in a round wall. So I casted a door from one of the other flat molds, along with some stepping stones.
Then added some Sculpey oven bake clay to blend it to the rounded architecture. I was a little afraid of the glue melting or the plaster cracking in the oven, but it was fine. I even forgot about it & it was cooking 20 minutes longer than it should have been! :-P
Add a little paint, a base, a little turf, & a banner then it's all set to go.
One note about the turf: I like to keep a 'dump jar' of all my flock/turf/dirt/what have you and use that as my base of Earth.