I often draw directly on to MDF as well, if you draw on paper, you either have to stick your paper plans to MDF to cut it out (in which case, you've lost your paper template anyway) or you have to trace the paper plan, then trace it again (or you end up with a mirrored plan), before you can transfer it onto MDF. If you've got a photocopier that will do A0 then fair play, but I haven't.
If you're building a common design, like a strat, tele, les paul, prs etc. Then I would consider buying pre-made templates. They're only about £60+ and will save you a lot of time, ensure accuracy on your neck taper and won't cost that much more money because enough good quality MDF will cost probably cost you £30 from a DIY store.
I've got some acrylic template from G&W and they're excellent. Acrylic although slightly more money is better than MDF because you can see through it. There is also the option to clone the templates and sell them on.