In a large bowl, cream butter and sugar until light and fluffy. Beat in the eggs, oil and vanilla until well blended. Combine the flour, cocoa and baking soda; add to the creamed mixture alternately with water, beating well after each addition.
Pour into a 15x10x1-in. baking pan coated with cooking spray. Bake at 350° for 18-22 minutes or until a toothpick inserted in the center comes out clean. Cool completely on a wire rack.
For creamy layer, in a large bowl, beat the shortening, confectioners' sugar, milk and vanilla until fluffy, about 4 minutes. Spread over top of cake.
For frosting, in a small heavy saucepan, combine the sugar, butter and milk. Bring to a boil over medium heat, stirring frequently; cook and stir 2 minutes longer. Remove from the heat; stir in chocolate chips until melted.
With a hand mixer, beat frosting for 2-4 minutes or until thickened. Gently spread over the top. Store in the refrigerator.