Ah, if you plant a crop right in front of a door, that actually counts as indoors (hence why the roof disappears when you stand there). I'm not sure how important this is tho - as why would you plant a crop right in front of your door?
You can mark multiple areas you want (the minimum cost is based on the size of the region, so it's more or less the same cost for a few small areas vs one big one if you want an irregular shape). It'd be complicated to exclude individual tiles, but I could just add a rule for no planting crops in the corners around trees/blueberry bushes.