Then why don't you?
No, really, why don't you? Right now.
http://beej.us/guide/bgnet/output/html/singlepage/bgnet.html
http://developer.nvidia.com/physx
These are the (free) tools that I used to build something very close to Quake. If a dummy like me can, then so can you.
And if it's your fantasy, then you owe it to yourself to make it your reality. Go achieve what I didn't.
I think you're more capable than you give yourself credit for.
I'd rather strike out a dozen times than watch from the stands.
To avoid getting down voted here are what I would call modern, or at least more comprehensive versions of those links.
http://www.unity3d.com http://www.udk.com http://mycryengine.com
If you really want to role your own engine then...
http://www.arcsynthesis.org/gltut/ http://msdn.microsoft.com/en-us/directx/ http://gafferongames.com/networking-for-game-programmers/ http://www.jenkinssoftware.com/ http://bulletphysics.org
Although a handful of links can't sum up the amount of work, knowledge and tech required to build something resembling a modern 3D game engine.