When you have to build large scale buildings can be a great help to create something like "preassembled component".
i don't know, something like: the first conveior, a splitter, 2 smelter, 2 constructor, a deposit, the floor.. you build the first time this thing and then you make it as a "group of things" and you past/copy.
even if you have to make a large floor i think it's usefull to select a 3x3 pavement and replicate it.
even better if you can create something like a "object" like a closed box. something with an entrance for resource and an exit for the stuff created. stackable and easy to deploy