...In all seriousness, we are meeting with the contractor this week to start making concrete plans (no pun intended) and already have a couple of possible layouts in mind. It will all depend on cost (did someone say something about money?). Once the building location is marked off, then I can start planning the paddock and pastures.
If you haven't already, think about if and how you are going to get water to the barn. If you will bury a water pipe from the house or somewhere else to get to the barn, at least a section of it will need to be in place before the concrete pour.
My plan, to prevent me from having to heat the whole barn to keep the pipes from freezing, is to install a cheap deep sink in a small cabinet in the barn. The water supply pipe will come up under the sink, and the cabinet will be very well insulated. Once that is done, you can heat that small space with just a thermostat and a light bulb (as long as no one leaves the cabinet door open when it's zero).
Down in that cabinet you can also install a point-of-use electric water heater for the hot side tap. They are small and cheap. Hot water in the barn is great for hooking up a hose to the deep sink spigot and giving hot baths on days when you don't want to risk chilling the horses.
in that cabinet you can also have a couple hose connections that will allow you to run heated water hose to heated automagic water feeders in the stalls. You won't want the sink too far from the stalls because heating any kind of water pipe costs more the further you run the pipe.
Finally, you mentioned heat. I see you are in Canada. I would put a lot of thought on your barn, and specifically, stall construction. You can spend a ton of money heating poorly insulated spaces, and when it comes to heating, smaller is better. Since the concrete guy is coming, you might ask about in slab hot water heat for the stalls. You can build one of those systems using a common water heater, and put the heat just where you want it, in the stalls.
Good luck and have fun. We're going through the same thing right now.
P.S. Get the pitchfork now...it comes in handy for shovelling the money out the door.