Thought I would share with you all who may be venturing into digital sculpting a quick little way to get armor pieces roughed out( can also be used for clothing ). This is not the defining way to make armor and clothing pieces in zbrush its just the way I choose to do it, hope you find it helpful.
1. Subdivide your model a bit, a couple thousand polygons is usually good. Mask off the area where you want the armor piece to be, in this case I chose the shoulder. In the subtool tab expand the extract tab, the only setting to worry about in here is the thickness. Adjust it to what you need then hit extract > accept to create your subtool. Shape as necessary with the move brushes.
2. Once extracted select it in subtool tab and clear the mask from it( all extracted subtools get a mask by default ) and then turn on polyframes.
3. Place your cursor over the top part of the armor and ctrl + shift + L click to hide the sides and bottom. Then in the geometry tab expand the modify topology tab and select delete hidden.
4. You will notice with all extracted subtools the edges are pretty messy. To fix this expand the deformation tab and drag the polish by features tab all the way to 100 as many times as needed. This will smooth out the edges.
5. Once you have you edges smoothed out expand the geometry tab and then the edge loops tab. Under edge loops scroll down to panel loops( For this example I'm using the settings I always do but feel free to experiment. ). Beside the panel loops button is a tiny loop slider, set this to 1, beside it is the "double" button, this will create an underside to your mesh. I set it to off. Below that a bit is the thickness adjust it to what you need for this example I left it at default. Below that is the polish slider, set this to 0, below that is the bevel slider also set this to 0. To the right is the elevations slider +100 means the panel loops will expand away from model -100 means they will expand towards the model. For this example I left it at +100 default. Once all your sliders are set hit the big panel loops button.
6. Now ctrl+shift+click on the newly created panel loop to hide the top part of the armor.
7. Adjust the thickness in the panel loops tab if need be but leave other settings to what you set them to previously. Hit the panel loops button to create a new loop.
8. Now ctrl+shift+click on the new panel loop you just created to hide the rest of the armor.
9. Now in the panel loops tab in the loop slider set it to about 5, adjust the thickness and bring the bevel slider up to about 20. Hit the panel loop button.
And there you have it
hopefully this will be useful to some. The same methods can be used for creating clothing as well. If you need your armor pieces to have more sharp/straight edges after step #3 you can use the slice curve brush on the armor to create more polygroup sections and then repeat the process from step #3 to delete the newly created polygroups giving you a more sharper form. Play around with the settings and most importantly, have fun. Note, when creating panel loops on a mesh zbrush applies a mask after you hit the panel loops button, make sure to clear each time before proceeding.