Think it through thoroughly, measure it up twice and do it properly once. Critiquing your designs for the unintended consequences and missed opportunities. Energy, daylight, ventilation and resistance to degradation. Design beyond the aesthetic.
A design tutorial can help with generating full plans, or modelling ideas using Sketchup or graph paper. How about tidying up that space and mocking up how to best use it. Lets get it built on paper before beginning. Don’t beware the temporary measure, it can be a very useful route to ensuring you are getting things right.