Summary
A simple Quality-of-Life feature to fasten and improve building repeated structures or patterns. Just point with the mouse at the item you want to build and press "C" or "." or some Mouse button and you get a copy of the targetted item to build just like if you have gone through the build menu (Q) and selected the item to build.
Disclaimer: This is not about Schematics/Blueprints to copy hole factory plans at once. For this a lot of other suggestions are already made. This is just a super simple feature which would even be helpful if there would be Blueprint-/Copy&Paste-Mechanics in the game.
Detailed
Problem
We often repeat building things because the building-patterns people use for factories and structures tend to repeat themselves often. There is one thing that slows down this process when you switch to another item you need to open the build menu with Q all the time.
If the players is lucky it's an item he assigned to the hotkey and just click the number, but often the specific item was too uncommon and not worthy of one of the slots. So eventually you end up again in the build menu.
If you have bad luck you need to even click into another category first before you can click the wanted item, more time lost and longer and more mouse moves and clicks.
Of course you could assign the items to the Hotbar, but there are only 10 items space and player don't want to change the assignments every 5 minutes because another set is not required. And even if there were more slots and/or more hotbars there is always an item which is missing and switching hotbars needs even more clicks and/or more shortcuts. So you probably still end up in the build menu anyways.
Suggestion
Just point with the mouse on the item you want to build press "C" or "." or some other button or the mouse (should be made assignable under Options>Controls) and you get the item to build as you would have by going through the build menu first.
Benefits
It's a very simple, very easy, very fast and efficient build method, especially since we repeat the same pattern often. Almost every build game introduces this kind of feature and it's often very well received and more used than the build menu selections or even hotbar-items.
