Warning, typos and mistakes are ahead. Writing from my phone.
If you look at the high-tech obnect, you will find:
1. Materials. Raw materials, which, obviously are to be gathered, and the bigger your object, the more of that you need.
2. Material technology. Raw materials are nlt simply cut, molten, glued together to make a detail. There is a huge variety of machining, pressing, forging techniques that are REQUIRED to make a detail with NEEDED properties. Drilling an inch hole is one thing, but try to make a 10 inch with a good precision.
3. Detail construction. Basically, whenever a detail is getting damaged, especially if it is an important detail that works under load, the only way is to recycle it. You can not fix it, like many other things that got damaged even slightly.
4. Detail arrangement. Basically what people understand under a "blueprint". Just have to say that construction is described by drafts (BPs), documentation, which includes the manufacturing, the assembly, the maintenence and so on and so forth. The "Blueprint" part could be imagined in a pile of thick journals, say, a meter tall when put one on another, when it comes to something like a battleship. Could be more. Transcontinental aircrafts consist of 1-2 million of details. Considering that future spaceships are to be more complex, I could only guess that things will get worse.
5. Manufacturing. There are good examples of RL tech that once being disassembled could not be assembled back without knowing the manufacturing technology. You just can not without damaging the object.
6. Resistance. Statical and dynamical loads, forces, torques. Take a wrong material, or wrong shaped detil and it will serve less than its original counterpart. If it will work at all and won't explode damaging surrounding stuff with shards. As for dynamical loads - cracks, they tend to grow, and do so until all of sudden things get really bad.
7. Maintenece. It takes time, it takes human power, it takes credits. If you don't know how to maintain you ship (the biger - the worse) it will eventually let you know when something brakes down.
8. Electronics. When damaged is to be recycled. You have your hull without brains, you can put new ones, but how would you write the software that is recognized by systems and that is working by correct algorhythms?
9. Something else that didn't cross my mind.
All in all, to develop something like a battleship from scratch it'd take centuries of experience, billions of credits for expensive research, modeling, absolutely expensive tools and facilities (And you can not assemble something big without precisely positioned mounts), labour, fails, tests, improvements, and all over again. The best you can do is:
1. Take damaged hull apart.
2. Make a frame of cheap modules, bought from dealer, that are produced on facilities and are open to market.
3. Slap hull parts over the frame.
4. Waste time, money, labour and end up with something like Bustard: huge but weak and powerless. Something that is far from being of a state of art like warships.
5. Try to sell it for ridiculous price (like Bustard) so yoiu could earn at least enough to cover expenses.
6. ???
7. Profit? No. No profit.
The same applies to anything but, say, racing vessels or something really tiny. Fighters are no, they are a state of art. You can not do a state of art unless you are a corporation with decades or centuries of experience and possess billions for expencive facilities to produce and assemble stuff.
What a group of junker enthusiasts is good for? They possibly could make some custom racers or utility ships. Again, buying frame and modules, because you are very unlikely to salvage something that dies in space (it does so violently), and slapping over hull parts, fins, etc.
This is my input on this matter. I have used some tiny bit of my studying knoledge here.
