DotA Items
There's a wide variety of items in DotA. In order to make the most powerful items, you must combine items, and merge them inte new ones using Recipes. There are four merchants selling recipes in each base.

Level 1 Human Recipes
Level 2 Orc Recipes
Level 3 Night Elf Recipes
Level 4 Undead Recipes

The higher level on the recipes, the more the items needed cost, as well as how powerful the items get. Sometimes, you don't need to buy the recipes, since the items merge by themselves. Otherwise, you need to buy the recipe.
this is the lates item chart i can get