So this is a guide for the Top of the World achievement in Minecraft bedrock edition for those people who want to go for it in their existing worlds instead of loading someone else’s premade save.
Calculating your resourcesFirst up we’ll need bamboo and string. If you’ve been playing for a while you probably have a ton of the latter but the former might be an issue. If you’re low on string we can point you in the right direction for that too.
Each set of six scaffolding requires six bamboo and a single string, the world build limit is 255 with layers 1-4 being bedrock, so if you start at the very lowest part of the world you are going to need 250 odd bamboo.
Edit: As mentioned by Madtown b below, only the top block of your tower actually needs to be scaffold. You can build a tower of whatever you have on hand and as long as that top one is scaffold you will pop the achievement. If that's the route you intend to take then you will only need six bamboo.
I’d recommend finding a nice tall hill or mountain as your base of operations for this project and work out how high you are already using your y coordinate either by turning on your coordinates in the settings or using a map. From that height you can work out how many bamboo you are going to have to gather for your monstrous construction.
If you are building from the shore of an ocean for example (Sea level is at Y 62) , you are going to have to go up 188 blocks which is just short of 32 batches of scaffolding (188/6 = 31.3), you’ll need 192 bamboo and 32 string for that project.
Finding your resourcesNatural bamboo generation: As a plant in jungle biomes, in jungle temple chests, as a drop from killing pandas (you monster).
Natural String generation: Drop from killing spiders, cave spiders and cats, collected from spiderwebs, tripwires in a jungle temple, dungeon chests, desert temple chests, woodland mansion chests, pillager outpost chests (pretty much everywhere).
I had issues finding any bamboo growing in the jungle for my world (3 days in game exploring and I found none), I did however have luck with the jungle temple I stumbled across which had 2 bamboo in a chest. That’s where I advise you search for bamboo if you are struggling to find it growing. Each jungle temple chest has a 50% chance of having up to 3 bamboo in and there are 2 chests per jungle temple.
To find jungle temples I used the chunkbase jungle temple finder page.
https://chunkbase.com/apps/jungle-temple-finderType in the seed for your world and click the “Find jungle temples” button and the program will work out where jungle temples should have spawned in your world, if you head towards them and discover a load of bamboo on the way, result, if not at least you know that you have a high chance of getting bamboo from the chests there. Remember to switch the version tab at the bottom of the map to “Bedrock edition” or it’ll generate for the java version.
Once you have as much bamboo as you feel is realistic to gather from the nearby temples, head home and plant the stuff. Bamboo grows fast and can be sped up further by using bonemeal on it. Bamboo has 4 stages to growth and will give you the most resources if you let it reach full height before harvesting all but the bottom most block with a sword.
If you are short on string, the chunkbase also has a locator for dungeons and other generated structures, my advice would be to use the mineshaft finder to locate a mineshaft as that’ll net you stacks of string from killing cave spiders and chopping up the nearby webs.
ConstructionOnce you have all of the bamboo you need the rest is pretty straight forwards. Build your scaffolding on a crafting table and start stacking up with your scaffold. I took a bucket of water with me to give me a fast way down but you can just crouch back through the scaffolding if you would prefer.
Edit: it's been pointed out that you don't actually have to climb the scaffolding, you can place the blocks from the bottom without having to stack up. Though you would miss out on the view then.
If you can think of any other information which I should include in this guide, please let me know.