Doh, it's in the title. Apologies, "extension cable".
Some old CRT monitors might be damageable with bad sync pulses, but I think that's about it. You probably want to use coax cable of the right impedence for VGA for each of those signals, otherwise you will get a blurry/bad mess on the other end.
I recommend cutting open a shorter VGA cable that you don't care about and having a look inside, see how it's made.
If you don't provide the EDID wires (marked as N/C in your diagram): you will have to manually force a resolution/mode on your computer, as it won't be able to auto-detect the monitor.
How long of an extension do you want to make? After a certain distance it's really only practical using active (powered) VGA repeaters.