This feature would be very useful for reentries with Deadly Reentry installed. Also for space shuttles.

Additional comments by @Neon-Samurai (on issue #76, which I'm closing as a duplicate):

One thing I feel that is really missing is the ability to set our roll when using smart ASS, we have heading and pitch in the surface tab, but not roll.

Mechjeb also frequently fails to orient the craft to wings level (0 roll) when surface mode is active. I have frequently had it either not adjust its roll at all, or randomly select roll angles from 0, 90, 180, and 270 (seems vaguely based on the hdg entered).

It would also be nice to have the option of having a roll setting for the ascent guidance page so the craft can properly orient itself on its own during liftoff.

This should be fixed by 4606fc6, which is in the following dev build: http://jenkins.mumech.com/job/MechJeb2/29/

Looks like that should take care of the SmartASS at least, yeah. Maybe once the steering issues are in a better state, the ascent autopilot can be re-tweaked to try to hold either a certain roll orientation, the starting orientation, and/or an option to have it maintain a continuous roll to help with booster separation. But perhaps that should be a separate 'enhancement' issue?