First, I went into Maya and created these four shapes on the plane. I loaded up Arnold so that it was available to use. I added directional lighting and the create skydome layer in the Arnold tab. I then went into the attribute layer and changed the exposure. I used the Arnold Standard Shader on the sphere, cube and cone. I made the sphere shiny by changing the weight in the attributes and specular. For the cylinder, I used the utility shader and added the wire using the material attributes, overlay mode and polywire. I shift clicked the objects and created a new layer (AO Layer) in the render layers, adding the objects in as well. On this new layer, I right clicked the layer, selected overrides, create new material override and Ai Ambient Occlusion. I changed the render view to Raw as its better for Arnold. I then created another layer (shadow layer) the same way, but with the lights too. I changed the material of the plane to shadow catcher and edited the attributes to catch shadows and enable transparency.
I went to pPlaneShape1 and unticked the opaque option. I went to each object, into render stats and unchecked Primary Visibility. I made a third layer (objects layer) with the lights and objects but not the plane. I then saved the file in a new project folder. I changed the file name for the render in the settings to Shadows <render layer> using the right click button. On the options tab in the corner, I clicked options- render all layers in the square and checked keep all layers. I batch rendered it and took the images into nuke.
In nuke, I read in the images and created a constant node, making it grey. I merged the constant with the shadows. I then merged the merge with the objects. For the AO, I created another constant and made it white. I merged the constant with the AO and then merged that with the rest of the nodes. I then saved again and used a write node to save my composition.