I am by no means a cake decorator. I used to watch my mom decorate cake for my brothers school bake sales back in the day, so I had some idea as to what I was doing, but haven't done anything like this in 20 years. I wasn't about to mix my own frosting and try to squeeze it through those decorating bags... so I bought the pressurized frosting cans. They even come with a variety of decorating tips. I decided to start with the brick because the grass would come up against it at the base of the brick. I just sprayed globs of red frosting on a side of the upper piece of cake, then with a smooth butter knife that has been soaking in hot water... again, like the Jello, the hot wet knife will melt the frosting and make it smooth. I did this to all the sides and top.
I then lightly scored the frosting with the knife so that I could use that as a guide for putting the white frosting grout lines on. It took 2 tubes of the white frosting and a steady hand to grout the bricks.
Finally, it was time for the grass. I practiced various types of grass on the parts of the cake, that I had cut off earlier, till I was happy with the look of the grass. After covering the two grassy areas with green frosting, I outlined the grass to give it a nice finished look. Again, this was all done with the compressed frosting in a can with supplied tips.