I recall when William the Conquerer came to England he had pre-built motte & bailey castle components (wood) premade to quickly throw up defensive strongpoints.

Perhaps some 'lump' of quick to used 'base' materiale can be specified in various scenarios to cut some of the buildup time ?

Im with the current trend of ideas to make base building something that happens before the match begins. I'd take it a step further and really focus on how the layout of your base and what units you select to be able to build will impact how the battle goes. Keep the maps small and compact too, to force the action to begin quickly.