I don't know of any specific tutorials. I feel like a World Editor tool is best used with a game in mind. You could use something like Unity which has an Editor to make any game, but thats the reason to try out Unity. If you want to create your own, you need to think of your game or what you want to use it for, what features you want. And program it like you would any game.
Every world edtior is really going to have a few common parts.
-You need a way to visually see the world. Be it a 2D world or a 3D world.
-You need UI (buttons, dropdowns, textboxes).
-You need a way to import and export data. (meshes, the scenegraph, etc).
I just finished a custom world edtior for my 3D RPG game I worked on. RPG's need a ton of tools and features, so I decieded for one monolithic tool: my World Editor. I had features such as
-Placing Objects (Trees, Rocks, bridges).......
-Editing Enemy Data (Hp, attack, loot, gold, exp)
-Designing Quests (start text, end text, start NPC, end NPC, loot, gold, exp)
-Assigning Quests to NPCs
-Sculpting the Terrain (raising lowering terrain, smoothing, flattining)
-Painting textures on Terrain (Paint rock texture on side of cliffs, or a dirt road, or sandy beaches near the water)
-Desgning Items (Item stats like Str, Wis, Def, Attack, Agi, Int, equipment slot, icon etc.....)
Now, this was all very specific to my project. But using this tool, I could design the world, nay the game, exactly how I envisoned it. Down to controlling Stats for enemies and the quest lore etc...
Your game might be a platformer. This tool is probably way overkill and maybe something more tile based would be better? There are also some already made level editors you might try and look at. I think GameMaker is one? I could be wrong. Have a look at Unity as well. But if you are dead set on making one, think about your game, and what you might need. Decide if you want this tool to be generic so you could reuse it in other games, or if it should be specfic to your game and therefore you can narrow it's vision and scope down greatly.