Here is how to build a Minecraft character, In this how to guide you can find the dimensions needed to do the default character (Steve) or your own skin with Minecraft's specification.
To start you'll need to know the dimensions of your character, lets use each pixel as one Minecraft block, the image below will show you the block measurement needed.
|Steve block Spec|
The image below show's the frame work needed for our character, I did the frame with black and white blocks so it's easy to count the pixel/blocks.
|Pixel block frame|
|Reference & game window|