Actualy, there's more to Slime Spawning than just making a tunnel to the center. There are random chunks of land that they can spawn in; the best way to find them legitly, is to build big caverns near bedrock, light em, and hope a slime spawns. Otherwise, get a mod that tells u the location of the chunks

if you know how to get costom maps i know a good one with a slime spawner in it and it works

i can help you make one but you need to get 1.9 pre 5 and if you can try to make a server ill join and tell you the basics i used to be just like you wanting to see a slime i can help you ive found 1 huge one yesterday and 3 today

It's already been pointed out below that they only spawn in certain chunks. They appear in about 10% of all chunks, so in 160x160 room at slime level (thats 100 chunks) they will only spawn in about 10 16x16 areas. The hard part is finding where they spawn.

I recommend either plugging up or lighting up ANY neighboring caves up to 5-10 chunks from here. It is possible the amount of hostiles spawning in neighboring caves is using up all the entities (200 max) and leaving none left for slimes. I also recommend getting rid of that walkway cutting into the middle of the room and possibly making the room larger just in case. If that still doesn't work, then I have no clue.

i couldent upload file it to big anyways if anyone see problem in that can plz tell me :D