Are you sure you are referring to Hard Plan and not Technology crates?
Hard plan are these blue crate that contain a single blueprint of a room, once used, it's gone, if you want to build more rooms of that kind, you've got to buy more hard plans from a trader.
While Technology crates, which are green in color, once opened, gives you the ability to build the room (or manufacture it in your factory in case of skuzzer and goods technologies) as often as you want, at a cost. To build rooms acquired through Technology crates, simply right click on the ground and a menu will appear, listing the various rooms you can build.