Lightroom has a good black & white editor. By adjusting its various colour channels you can tweak the tonal range of a greyscale image and make it look like you photographed it in black & white.
Step 1: Remove The Colour
First click on the B&W button to remove colour.
Step 2: Darken The Sky
Scroll down to the HSL / Color / B&W section on the right. You will see a list of 8 colour sliders. If your shot is of a brick building (unlike ours) the main one that will affect the look of your image is orange, but you may find some of the others do stuff when you slide them too. For example, as we have quite a bit of sky in our shot, we can darken it with the blue slider. Simply slide the blue slider to the left and watch the sky go almost black. We don't want it too dark so a -20 setting is fine.
Step 3: Adjust Tonal Contrast
If you are working with a shot of a stone building adjust the orange filter to change the stone's contrast. This has a similar affect to shooting through an orange filter with black & white film. If you drag it right you will see everything lightens up, drag it left and things become darker but also more contrasty. Try pulling the slider to the left to around -40 and adjust from there as you need to.
Here's the before and after shots of brick work to show you what applying the orange filter does to brick work. The change is only minor in this shot but it does allow the detail in the brick work to stand out more. The difference is more visible in the middle of the shot:
The yellow slider affects the lighter aspects of the building and these we will lightened by dragging the slider to +30.
Step 4: Overall Contrast Change
Now scroll up to the Tone curve and lets set an S shape curve which results in more contrast. You will find you use this on most digital shots to boost contrast. Take the highlights slider to +50, Lights to +20, Darks to +20 and drag Shadows left to about -40.
You can now see a much more striking image with defined contrast detail in shadows but with much more depth: