First you need to have Mass construction unlocked, you can find it in the upgrades research tab.
The research tree has 5 tiers upgrades for the blueprint section. every upgrade increases the number of facilities you can copy at once. Level one you can copy only 60 and level 5 lifts the restriction and gives you unlimited.
Once completed, you should see a new icon in your toolbar.
How to get a blueprint's code?
You first need to create a blueprint in game. In the blueprint's toolbar, select the first icon:
And then select your facilities. Once you're satisfied, finish your blueprint by clicking save blueprint.
Click the Copy button in the blueprint screen.
You're done, the blueprint is now in your clipboard, and you just need to paste it in the form field when adding your new blueprint.
How to use a blueprint code found on this website?
Simply click the
button on a blueprint's page.
Then, in game, create an empty blueprint and then click on the new created blueprint.
click the Paste button in the blueprint screen, finish by clicking the save changes button.