Top down: grind down a material into its wanted shape but creates waste.
Bottom up: build slowly the intricate parts.
A solid method is to create the nanites in a combined fashion.
You’re building cubli’s.
Use: pyrolysis carbon casing to be safe incase of failure inside the body and allow available attachments to drugs or operating tools. Cancerous bone is weak. (I believe so you may not need carbide tips to get through if going slowly enough). Sewing systems can join molecularly within the body at attachment points similar to spider web sacks joining together in series and rotated out with a twist to the nearest neighbor to continue the feed until the suture is done.
Top down to manufacture housing and empty inside shell. A series of holes is drilled at each cross corner so as to not be totally flat, where you’ll later bond conductive material to electro magnetize those sides and corners using dip pen lithography.
Waste is removed continuously and recycled into pure material once atomic slag is removed if any.
Bottom-up using recycled innards plus additional materials to build control mechanics.
Molecular beam epitaxy to lay films of atoms inside the inner workings in specific orders or “shells” until all moving and inert parts are manufactured and in place as warranted. Will have to ask the creators or a computer optimization algorithm to find the best method. Battery cells will have to be dropped into place and connected with dip pen lithography again.
Build the system on a roll to roll “conveyer system” and you end up with the finished product at the end.
Test outside body on cancerous white blood cells with users artificial cytokines and antibodies. Or coronaviruses. Force them to encircle the viruses as artificial kill cells and use the batteries to heat the systems conductive materials with partial RBCs cellular make up on the drug attachment points that the corona wants to bond to and then heat to the viruses destruction point and the virus is eradicated from within with simple nanites. Remove dirty nanites from system. Clean. Repeat.