I just posted about a Plexiglas Cutter:
Now as to the Plexi you cut. You can go up to 3/16ths Before you need a saw. The idea is to get a clean Score and then use a clean sharp edge to do the break. You can do thicker if you want, But you then Better scribe BOTH sides and clamp before you try the break!
Now here's the thing, If you are trying to build a case for your model you definitely better make sure All your pieces are square! That includes the edges from side to side. This can be a challenge but doesn't need to be. If your break is edgy(fine shardy edges, back from the surface , this is no problem. Draw a line with a Sharpie.
Make it close as you can to the best part of the break as you can. Then run a sander over the edge from end to end and top to bottom. Keep checking your edge for square. That's from side to side! When everything is square, comes the next step. Polishing that edge prior to glueing.
That's how the pros do it! When the edge is polished and square then the glue used will definitely show you what Capillary action is. You will physically be able to see the glue run down the seam. When dry, You'll have a nice clear edge left behind! Everything square, clear and dry. Note: Do NOT Remove the protective paper until you are done, Just move it out the way and cut the excess off with scissors.