assembling the strip sets, adapting a pattern to a different size

We eventually decided on 7 strip sets total. This changed a couple times...

Be open to changing any aspect of your project at any step. Cut yourself slack if suddenly you realize that what you'd declared non-negotiable in color scheme, layout, or whatever is just not working. You want to love your project when it's done. :)

We're adapting a full-size quilt pattern to make a twin quilt.  How do we cut our fabric to get the right dimensions for *our* quilt? Which of the directions for the full-size quilt do we follow and which do we change? 
That requires... I'm sorry to say... math. *weeping*

If you are a visual person, I strongly suggest sketches and notes for each step. Labels, lists, whatever you have to do to keep things straight.

We chose a different color scheme than the pattern calls for (and changed it again, ack), and a different (but much easier, yay!) construction of the middle, narrower strips in each strip set.
So... we worked backwards.

What's the finished size of *our* quilt?
Are we following the pattern directions for strip dimensions and just shortening the finished strip sets? (yes)
We decided to make our quilt half as wide as the pattern.
The directions are Right There, and I stared at them for a very, very, long time. LOL