So I built a simple zombie XP Farm and the problem is that the zombies wont spawn unless I'm standing above or in the hole. It's annoying I just want to be able to do something else then go back and kill all the accumulated zombies. If anyone has any solutions to this problem, it will be appreciated.
One solution is to create many farms and different work areas around spawner.
For instance, next to spawning area i have crafting table, enchantment room, anvil, furnaces, infinite water source, small wheat/potato/carrot farm, brewing stand, nether wart farm, small tree farm, outlets of automatic sugar cane, melon, pumpkin and cactus farms, area to grow mushrooms, half-automatic seed and flower farm and front end of storage room. Tree farm is also good place to use fortune pick on collected ores. You can fit small cobblestone farm and obsidian (using redstone) farm as well. Even building those things gives you lot of XP from zombies. When they are ready you can work around your spawner and collect lot of additional resources.