If you're new to Warcraft 3 map making, you should probably start by checking out the tutorial section:
WarCraft III Tutorials
There you should find a lot of guides that will show you how to make great terrain, including things such as houses or dungeons.
For example, these tutorials explain how to create an "enterable" structure:
How to make directly enterable houses (no dummie houses)
Enterable Buildings
These explain how to make a decent dungeon:
Creating a Dungeon Entrance
How to Make an Epic and Worthwhile Dungeon
And these are some general guides about making a nice looking terrain:
The Ultimate Beginners Terrain Tutorial
Natural Environments
Advanced Terraining Tutorial
Browse through this section of the tutorial forum to look for other tutorials on general map-making and terraining:
General Mapping Tutorials
Also, if you are completely new to Warcraft 3 map making, you might wish to first check out some of the basic tutorials such as this one:
A Beginner's Guide to Map Making
As for triggers, be sure to visit the GUI tutorial section:
Trigger (GUI) Editor Tutorials
Since you are a beginner, some basic guides can be found here:
Basics of Triggers
Chaosy's GUI tutorial for beginners
Basic Triggering
Complete and Concise GUI Tutorial
Once you learn all of that, you can move on to some a bit more advanced stuff such as implementing game systems or designing AI. I will not post any links to guide on these topics here, but if you wish to check them out anyway - just head over to the tutorial section
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And... Remember that what I've posted are just some examples of the useful tutorials that are available on the Hive. You can find way more in the mentioned tutorial section
At any rate, follow the tutorials and you should get a general idea on how to create a map - the rest is pretty much up to you. With some experimentation and time you should eventually get there and be able to create a decent map, be it an RPG or something else.
