looks like you got some pretty nice huts,if i could make one suggestion,don't know if it would work,or if it would even necessary.but pour your pad as you propose,then build a oak or some kind of a wood platform for the huts to set on.the reason i recommend this to keep the hut dry,even if you bed alot and turn the girls in and out,moisture in the hut is your enemy.and cold concrete can chill the piglets pretty quick,although brooder heat will help out tremendously.the only drawback to wood is that it is hard to clean and disinfect.i'm basing my suggestion on my local experience,if your location is more arid and temperate might not be that big of a deal.