Let's say you want to build a house. If you know what you're doing, you could put together the plans, get the approvals, order the materials, and hire various contractors to get the work done (masons, carpenters, electricians, etc)

In that case, you are acting as your own general contractor. If you don't have the skill to do all of that, you can hire a general contractor to do those things for you. In that case, you are approving timeframes, designs, materials, and money. All this is based on what the GC is saying. You are working at a higher level, and paying for their expertise.

However, you have to also determine if what the GC is saying is realistic, as well as if what you are asking is realistic.

If the GC says they can build the 2000 square foot house for $20K, they are not being realistic. If you require that all windows be bullet proof and cost the same as normal glazing, you are not being realistic.

Either way, you're ultimately responsible, just like the state of CA is for building this rail line.

The short of it is, unless you know what you are doing, don't get involved in building a house. Buy one that is already built and get a good inspection.

There's a difference between owning the job in organization and farming it out completely. You don't need to have all competencies inside your org, but you better have some kick-ass people you can trust that can ensure you're not scammed by external consultants - or who know how to talk with contractors so that the project is not catastrophically buggered by nonsensical behaviour and unrealistic expectations of your org