Good question. I wish some one would answer it. sept 2018 and still no answer

only way for you to build blueprints is to build them from memory.
there is no current feature there allow building blueprints in survival.

you could suggest it on the official keen support site on the feedback section.
with maybe your idea on how it would work.

https://support.keenswh.com/medievalengineers/

Myself and house have had the same brain storm - the only idea we were able to come up with was maybe making a blueprint of it in the blueprint table and being able to place a projection of it to build (auto deletes on server restart)