I've got the idea that some bands don't march because they can't afford drill design and the director doesn't know how to write a marching band show.

A stock show can cost hundreds of dollars and custom drill is even more expensive. Drill design software is also very costly. 

While a young teacher working with paper and pencil probably isn't going to create the next new trend in marching band show design, if you're in a school that hasn't marched, and you don't have a budget for drill, you can accomplish a lot by watching other
bands on youtube and sketching your own drill on paper.  This page exists to show you how to get started.  From there it's a trial and error process.
To get started you'll need a few tools.  First of all you need to plan your lesson time and analyze your music.  The drill and show design link on the left can help you with that.  Then you need to decide what kind of maneuvers you feel comfortable teaching.  Those are the ones you can write into the drill.

Then you'll be ready to put pencil to paper and create a marching band show.

Click the linked picture on the right to download blank drill design paper.  The pdf file requires Adobe PDF reader to open. Then you'll need to print it.  Printing it on legal sized paper at 1200 DPI is best.  Then you can use a copy machine to enlarge it to 11"X17". 

Make A LOT of copies, then plan on using a sharp #2 pencil for sketching and a razor fine sharpie for last draft "inking in."  After you ink, you erase the pencil marks.  This is the way people wrote drill in the decades before computer aided design.

You'll also need some drawing tools. 

Here's the bare minimum:

A straight edge - I like the clear top of an audio cassette box.  It has a cool built in handle and you can see right through it.  Best of all, it's not only free - you're recycling!

You'll need some kind of french curve tool.  Click the linked image to the right to see more.  You can also find them at most dollar stores and supermarkets.  The usual price for a basic french curve tool is a dollar or less.

Lead core flexible rulers are available from some office supply stores, drafting supply stores and art stores.  They're handy and fun, but I don't think they're worth the price.  A good one will cost you $15.00 plus shopping time.

Then You'll use a folded sheet of drill paper to measure stride size and interval.  Pick one basic interval and stick to it for the whole show.  If it's a two step, you can mesh to a one step and unmesh to a four, and you can skew a line so that they're in a diagonal that goes two up and two over.  Keep it that simple and your home brewed drill will be teachable, cleanable, and fun to perform.

One more thing - if you need free advice, don't hesitate to call . . .
the college professor who should have taught you all this in a methods class.

There are several books that are very helpful drill design resources.  Dan Ryder's books are great and Bob Buckner's is an essential read if you can find it.  Both of those guys were doing great pencil and paper drill before I was even in beginning band.  Don't be afraid to stand on their shoulders.  We all do. They're the giants of drill design.

Good Luck!