Adjust tone and the color of the image a little bit. Go to > Image > Adjustments > Hue/Saturation (Ctrl+U) and reduce the Saturation to -89. Then go to Layers panel, create a new adjustment layer and select Level. Make sure you turn on the Clipping Mask button and set the settings as shown in the 1st image. Now Go to > Layer > Layer Style and select Color Overlay, or you can also simply clicking the (fx) icon in the Layers panel. Apply similar settings in the 2nd image below.
When you analyze the image of a Man, the light seems to come from the front, and when the object is further from the light, it should get darker. So the idea is to keep the darker part of the Metal texture further next by the Vault.
Before we go to the next step, turn off the layer visibility of Man layer by clicking the eye icon in the Layers panel. Open the Metal Texture image, and drag it to our canvas. Press Ctrl+T, right click in selected area and choose Distort from the menu. Go to > View, and check the Snap option. This will help us to snap the handles precisely to another object while dragging. Now drag top left corner of handles to the top left corner of canvas, and the other one to the top left corner of the Vault layer. Then Go to > Image > Adjustment > Levels and set the setting as shown below.
When you are done with one side, create the other one by copy the layer. Simply drag and droping it into the new layer icon of the Layers panel. Then again, press Ctrl+T, right click, and select Flip Horizontally. Repeat the process with the same technique to create the ceiling and the floor.
Now you see, the Vault still does not blend well with the Wall. To fix that, Go to > File > Place and select Metal Texture image. This will automatically import the image as a Smart Object into our canvas. Put the Metal texture layer above the Vault layer. Press Ctrl+T and scale the image to fit the width of the Vault. Hold down the Shift key as you drag to maintain its proportion.
Now set the layer's Blending Mode to Soft Light. Duplicate the layer by dragging and droping it into the new layer icon of the Layers panel. Press the Ctrl+T again and put the pivot point to the top center of the bounding box. Then right click and choose Flip Vertically from the menu to cover the top area of the Vault.
Let's turn back on the visibility of Man layer. Click the Add Layer Mask at the bottom of the Layers panel and start painting with soft black brush preset to get rid parts of the body. No need to be precise, as we can fix that up later. The advantage of using the Layer mask is that you can always come back and edit any adjustments you've made previously.
Now with the adjustment layers, select Hue/Saturation. Set the Hue to +12, and reduce the Saturation to -70. This will give the Man a lot more blended look with the background. When you have configured the settings, make sure a clipping mask is applied to the layer.
Now let's focus on shading the backround and add some depth. Load the selection of perspective guide layer by clicking on the layer thumbnail while hold the Ctrl key. Add a new layer above the Vault layer and grab the Gradient Tool (G) on the Tool panel. Press and hold Shift key, then click and drag from the left to right on the left edge side of the Vault. Reduce the Opacity to 39% and set the Blending Mode to Multiply. See the 1st image below.
With the same technique, repeat the process on the right and bottom edge of the Vault. As you can see, the bottom area of the Vault is lighter than the other area, so we need to darken it a bit by increase the Opacity to 60%.