How Do I Make Art for Mod?

Just as the title suggests. How do you make 3-D art for tile improvements?

How do I make the art to use for my custom civ that I will use for a tile improvement? Also, how do I make the art for leader image? Not the icon, but how do I make the 3D improvement art and the 2D (but intricate) leader meeting image?

Moderator Action: Two posts merged - please don't set up multiple threads that are essentially about the same thing - if you want to add to your request, simply amend the post.
Please read the forum rules: http://forums.civfanatics.com/showthread.php?t=422889