I needed bricks to fit my hipped chimney. I started by cutting a piece of paper roughly 1/4" wide, which is the finished measurement of my miniature bricks. Lay it on the space you are making a brick for, keeping a little gap between it and the brick next to it for your grout line. Bend it at the edge to get your angle.
I cut it along the angle using the Xacto knife, then I held each piece where I wanted it with poster putty. I also used a little bit of putty to hold them together so I could keep the shape when I peeled it off. I colored it in with pencil so you could see it better.
Take your paper off and trace it onto egg carton. I had to adjust the height to make each side the same, and this is actually a little more than 1/4". I just trimmed it down after I cut it out. I also traced a second one so I had a template for the rest of the bricks.
Flip your brick over and score along your angled fold line with the back of your Xacto knife. I also traced this with mechanical pencil to show the line better.
Glued in place.
Now to do this half a dozen more times. I plan on using the same template and just adjusting the length of the longer arm.