Playing on Win 10 edition and finally got my villager breeder working correctly and then built my iron farm.
It's working correctly except for one issue, the golems fall down into the lava nice and proper but they don't drop thru and past the ladders I am using to hold the lava up, they get hung up on the top of the ladders, so I tried signs, those burned up from the lava, so I tried trap doors and the iron golems quite often again get hung up on the top of the trap doors, yes the trap doors are open, I'd say it's about 50/50 on them falling thru to the correct spot of the kill zone. Not sure what else to try except maybe pistons just above the lava on all for sides to try and bump the golem into the center so he'll drop the rest of the way
I had the same issue with my iron golem farm when (1.1? 1.1.3? I'm not sure) was released. There is a solution. It turns out that lava source blocks don't set fire to signs beneath them, only flowing lava sets them on fire (and maybe only if it's beside them, not above them--I'm not sure). Place signs in every block at some height, then place a cobblestone on top of each sign. One by one, replace each cobblestone with a lava source block. You have to do each one quickly, before the adjacent lava source starts to flow, or the sign could burn.
Unlike ladders and trapdoors, signs have no hitbox for the golems to get stuck on.
BTW, the 1.2 changelog claims that signs will no longer burn. I haven't tested that yet, but if it's true it means you won't have to do the cobblestone replacement trick any more.
trapdoors and ladders are bad ideas in general too much could go wrong and yes the sign's are fixed in the B2Ubeta so far. always use signs unless you need to block the path of something. YOu could also use magma blocks in place of lava, it takes a bit longer to kill but it saves resources and its easy to set up
Finally found a year old youtube video that resolved my issue with signs burning up. The trick on Win 10 is Hoppers then signs one the next level and then another level of signs above that then the lava on the 3rd level above the hoppers. Apparently the air gap below the signs caused the lava to burn the signs, placing another set of signs below them removes the air block/gap/whatever and this prevents the signs from burning up, supposedly the signs have no hit box for the golems to get hung up on and so they fall thru correctly and stand with only their heads in the lava thus not causing the loss of ingots in the lava. Much thanks to JackFrostMiner of YouTube for this video, testing it out now and working, just double checking the hit box of the signs before I call this iron farm completed