I'm trying to make an outline/shadow of a wall e that has several layers. What do you recommend to do so?

Could you give us some more details?
I don't understand what has several layers. Do you mean there are several layers in the image, or do you mean that the shadow or the wall has layers?
Is "...wall e that..." a typo, or are you describing a letter 'e' that stands up like a wall? If you have an image you could insert or upload, you know they say the picture is worth a thousand words

I'm trying to think of some general steps I could offer, but I'm sorry that I just don't understand the problem well enough.

Create a new layer that will hold the shadow. Duplicate all objects in each layer (or at least the ones that form the edge of the drawing) and move them to the shadow layer. Once you have them in one layer make a union of all of them, color it black or gray and blur, offset if you like. Move the shadow layer to the bottom of the layers list if it's not there already.