@BishopA cyborg that's mostly robotic is fine.
The thing about lightsabers is that you have to use the Force to create them (at least in Legends), so, while anyone could put the parts together, the efficiency would be too horrible for it to work properly unless you infused it with the Force. This infusion is what tied a Jedi to their Lightsaber, and gets rid of tiny imperfections that kill the efficiency.
In fact, in "I, Jedi" Corran Horn had to meditate on his newly constructed lightsaber for several days to make it work, even though the components were a few hundred credits worth of salvage and a crystal from a jeweled goblet.
Edit: We could say that you have an inferior version of a lightsaber (less damage, low battery life) if you wanted to just say you found the schematics and built one.
If they were easy to make, though, I feel like they would have been more common.