Isn't råspont unplaned on one side? There is hyvelspont which is nice on both sides. But anyway, with regular tongue and groove boards you probably don't get any lines like in the picture? Or is it if you don't tap together the tongue and groove then? In the picture, it looks like the edges are beveled, and thus the lines are formed. Or it's like on our old doors hanging here at home.
All types of wood will warp, more or less. You can definitely use raw board or other pine, but let it dry first. It should dry under pressure so it cannot warp. Alternatively, you can assemble the door and place it under pressure. Regular panel wood works as well.
If only one side is visible, you can cover an MDF with whatever you want it to look like. Otherwise, outbuilding doors tend to warp as they are often outside.... The moisture content thus goes up and down, causing the wood to warp.
