..a few examples below of treatments (proposals) I've sent to broadcasters.
There are no correct approaches to this - other than getting across your vision. Nowadays many development producers (or their bosses) send in, via a production company, a single page summary of the prospective film to a broadcaster and possibly fill out an online form with specific info - e.g. who's the talent/contributors? If there's interest, meetings follow and hopefully some funding to produce a fuller 'development' treatment on which production is considered. Most never reach production.
RAIDERS OF THE LOST ARCTICON (3 x 50')
This film didn't get made. Terry Jones (of Monty Python), initially keen as presenter, decided he didn't have the time. Channel 4 said no. As it happens, copies of the lost 'Arcticon' or bits of it are now surfacing. Here the one page version..
This is a more detailed development document I wrote most of for Independent Image many aeons ago. I'm not sure how many other people split the screen for sound and vision (it's not how feature scripts are written!) but its how we do it..