you don't need any engineering knowlege, just mathematical knowlege. The timbers are already oversized for the shed example in Jack Sobon's book. So you just need to change measurements, not timbersizes. I would recommend using the timbersizes in the example- you'll like them.
In this case if you need a 144 square foot building let's say you'll build it 10 X 14 feet
so instead of the bents being spaced eight feet apart you space them seven feet apart(or six and eight feet)
instead of 12 foot wide bents make them 10 feet wide.....
the same number of braces should be good.
if it seems beyond you to resize the measurements, find a math wizz or an old carpenter for some help, shouldn't take long
-M.
