Input plans into a CAD package, set units from English to Metric, voila! You're probably going to need to use the CAD step to get full size prints for templates anyway so just let the program handle the conversion. Building an aircraft without some form of CAD would be like building without power tools. Plus if you make your changes digitally it will hopefully minimize the efforts of making errors and having to make a new parts. By separating assemblies in blocks you can easily get full size prints of certain areas of construction and break down the building process in time and cost easier. Isn't TurboCAD fairly affordable? I know it's cross platform and should work for just about anybody.
http://www.turbocad.com/ $129 USD - compared to ArchiCAD or AutoCAD that is quite "inexpensive".
