G'day, Monica.
It means if you did have enough stone, then you could build up to four roads at once, but yes you do need to acquire the stones to be able to get the roads. If you don't have enough gold, then you could always try the lucky card for stone or gold (once every ten minutes or so). The roads last much longer than the Granaries, but they too are temporary (based on how often you play, though; the more you play, the faster things will wear out).
It's one stone per road, at The Castle.
The base rate for food production is six per hour (one every ten minutes); each road adds one food per hour, up to 22 roads (if you've earned enough meeples) for 28 food per hour. This means, if you did actually have 22 roads, then for your basic limit of 20 food to fully recharge the waiting time could be reduced from the full three hours and twenty minutes to just under forty-three minutes (one food every couple of minutes or so). To do all this (if you'd earned enough meeples) would probably only cost less than a couple of US dollars.
Your four roads, if built, could get you down to a total recharge time of only two hours (one food every six minutes). I think you could probably do this about three or four times over for the site's minimum purchase price of US$1.69. But most people who are going to spend real money would probably just pay for a period of Magic Potion and circumvent all this need for Food production (and patience) in order to keep playing whenever they want.
I hope that this helps. Any further questions, just ask, and I'll answer if I can.
