Also notably Roman roads were built by the roman government itsself, using the Roman Army. There were no contractors, bids, or private anything involved. It was 100% a government project. Private involvement was supplying the materials.

The US actually used to do a lot of this. Like until the modern Era the military manufactured all its own arms. Curiously enough until the Korean War the US also didn't do pointless proxy wars without clear military objectives. The way it worked is the government would commission private companies to design the equipment, but would run its own factories to build it itself. Thus the equipment was made to spec, and it was designed to a performance target instead of at lowest cost to a profit margin. WW2 was the first time they actually started to hire private companies to do manufacturing of arms and armor because of the extreme demand. And it would seem those companies really realized getting $billions from government was...kind of of nice.

IMO the government should be doing its own projects itsself. The whole contractor system is too ripe for abuse and corruption.