(Warning numerous Star Trek references)
There are four types of construction. The two methods that exist now are destructive machining and molding with extreme temperatures. Coming to a future near you it will be possible to use nanites to assemble from the atom up. In the future it may be possible to convert energy directly into matter in the form of our choosing like in Gene Roddenberry’s writings. The original Star Trek series avoided stories lines that dealt with the implications of this theoretical technology. Star Trek the next generation invented transporter limitations to avoid opening that can of worms, however in a few episodes they broke those limitations to tell the story. The rules they had in Star Trek tng for matter and energy conversion were inconsistent at best.
Two big rules they had to write in was that the transporter buffers had to have short-term memory loss and could not add any matter. They could however subtract matter, like a virus. In order to write a few episodes the ability to subtract had had to be ignored though so the Doctor could have some lines. Replicators could replicate food and small parts but no living things. Holodecks could turn energy into a form of matter that could only exist in the confines of the holodeck.
The transporters memory buffers could only temporarily store the data necessary to reassemble the energy into matter. The transporter could convert anything from matter to energy and back to matter. If transporters could add matter, that ability would have incredibly far reaching implications. What would prevent you from making copies of whatever went through the process? In one episode that broke the rules a crew member who had been genetically altered to age rapidly was returned to normal using DNA from before she left. This would mean you could keep backup copies of yourself in protected storage, creating snapshots at certain desirable ages, appending the changed data from the synaptic pathways every day essentially making you immortal.
If you could save a copy of the pattern and add matter, then you could of course replace tissue loss, or changed due to injury. No need for Dr. Crusher anymore, Troy would still have a job though. For that matter why risk injury at all just beam out a copy of yourself. Then step into the transporter, beam your copy back but only integrate the changed synaptic pathways giving you the complete memory of your copies adventures. Heck why beam a copy of your same ole boring self? You could be any creature or mechanism, real or imagined.
Everything we need could instantly materialize. A spaceship could be nothing more than a power source computer and conversion device. Then whatever ship design you wanted could be instantly constructed around the device and could adapt its construction on the fly to suite your needs. Damage could be instantly repaired.
Engineering entire solar systems, galaxies and even another universe would be possible with enough power. Then Humanity could have its own little worshipers to love and keep us company.