Does your school have a drafting or
CAD class? When I was in high school, there were classes in both
hand drafting and
CAD and we had a teacher and computer lab for it. It was not run by the
theatre department, but I know many
theatre kids took the classes. That being said, I did go to a fairly large high school in a big city. However, you might want to see if your school has such a class, because if they do, you may be able to talk to the teacher and see if the school owns software you can use to make light plots. If it is the right teacher, they may even help you out. For that matter, you may want to take a
CAD class!
With the technical aspects of drawing a
plot aside, when doing any show, the
plot is not the key to good design, the concept is. With a show like Seussical you can almost do whatever you want in terms of design (it has to work with the costumes and sets, but you have a lot of latitude) because it is totally made up. You don't have to make it look real or period. It doesn't have to be super "dramatic," it has to be fun and creative. With this show, don't get bogged down in the technical details and drawings, try to come up with a fun, vibrant and exciting design. On a show like Seussical, the only limit to what you can do is your imagination.
My last
point is this: You can have a beautiful design and draw it in crayon on the back of a napkin if you have good ideas. Only a small part of design is about the
plot on paper, design is really about the feelings and ideas that you communicate through light. A
plot is just a way to communicate to other people where to hang lights, by itself or in the hands of another designer, it can be mostly meaningless. You don't need a computer program or super
hand drafting skills if you can find another way to communicate your design ideas effectively. So, if you are designing the show, design it, worry more about how it looks on
stage than how it looks on paper!