I need to render my edited 4K multicamera footage to 1080p as a Quicktime or Prores file so a production company can edit it further. It will be eventually played in a large room for 10K people so I want to deliver a decent quality to the editors.

The quicktime templates provided in Vegas 12 are not high quality settings. I also don't see a Prores option under the render options.

Any suggestions for how to create a high quality QT or Prores file for my customer?

Jeff, as you've already found out, Vegas does not give us a ProRes export option.
The best solution I've read is for both parties to install and use the free Avid DNxHD codec. Versions are available for both PC and Mac.
Vegas guru John Rofrano has a tutorial (and download link for the codec) for Vegas users on his site at Avid DNxHD Template for Vegas Pro (http://johnrofrano.com/training/video-tutorials/avid-dnxhd-template-for-vegas-pro/)

Worked like a charm, Mike! Thanks so much! Tutorial was a snap. I was in a bit of a panic as am supposed to deliver today! It's all good now, thanks again!

Jeff, I'm glad to hear that it worked for you. Happy editing!!

Editing and render is done, delivering to client this afternoon! All is well, thanks to you Mike (and John Rofrano!).

Glad to hear that Jeff.

Thanks Mike! I was glad to find your solution and link. Very helpful

Phil, I'm glad I was able to help you too!!