Valve has announced , and released, the first alpha version of its Dota 2 Workshop Tools, which will make it easier for modders to make and share custom maps and game modes for their gargantuan wizard-'em-up. This initial release is targeted at developers, so the system requirements might be a tad high: you'll need a 64-bit version of Windows, a Direct3D 11 compatible GPU, and you'll need to opt into the Steam Client Beta. If you have all those things, you can now use the tools to alter Dota 2 to your liking, uploading the results to the Steam Workshop for other players to try.
As Valve explains at the above link, the Steam Workshop submission process has been streamlined as of this alpha release to allow players to subscribe to custom game modes, which will tell Steam to automatically update them on your behalf. To play custom game modes and maps you'll need the same specs as above, but Valve are promising support for 32-bit machines sporting Direct 3D9 down the line, so if you can run Dota 2 now, you should be able to run its mods eventually.
Seeing how the original Dota started life as a Warcraft 3 mod, it's only fitting that Dota 2 should introduce proper modding tools, and the possibilities are rather exciting. Time will tell just how robust and open to experimentation the new tools are, but many commenters on the Dota 2 subreddit are already hugely impressed, with one existing modder stating that the update is "like Christmas for all of us".
If you've been inspired to give the tools a try, you might want to read up on the extensive documentation first. The tools comprise a developer console, asset browser and the Hammer level editor, along with model, material and particle editors. Now go forth, and create the definitive edition of Pudge Wars 2 that the world has been waiting for.