my shed is a lean to extension of an existing brick outhouse. it was built without plans or drawings, basically making it up as we went. It's purpoise is to provide an area for my son and i to strip, repair and rebuild his first motorcycle.
The most important thing about this shed build was that it was undertaken by 3 generations of my family. As mentioned before the shed was built for my sons bike and he joined me and my dad in the construction process.
the most important things I considered before commencing was to condiser final dimensions before commencing. ie - the final dim of the sloping roof was considered before the footprint of the shed was decised to allow full sheets of 8x4 to be used for the roof. The frame was constructed to fit the glass panels previously aquired as a freebie from work. By all means make it up as you go along, but with a little pre thought it can make the end result more satisfying.