Going off of memory so may not be entirely accurate, but in SR4 you definitely needed;
1. Delta level facilities and staff, as well as a completely sterile environment for the duration of the procedure
2. A group of magicians, at least one of whom had mastered both Corruption and Invoking magic.
3. The procedure itself, which required a whole slew of steps to be completed roughly as follows:
3a Create formula and prepare the subject as a vessel
3b. Complete a metaplanar quest using a great form spirit as a guide (I think Astral Gateway was used, and the whole ritual was largely up to the GM to decide)
3c. Surgeries; minimum of an invoked memory stimulator (can't remember the essence and nuyen cost, would have to check later), but likely going to be a ton and likely all delta
3d. The Cleansing metamagic must be used to keep the background count in check
PROFIT!
Well, not quite. I believe the subject has to be kept in stasis for one week per Essence point below zero that's lost, and upon awakening there was some sort of test (Composure, maybe?) with the Binding skill of the ritual magic leader added as a positive dice pool modifier. I couldn't tell you the threshold, but I want to say it was relatively high, at least 1 per point of Essence below zero that's been lost. Succeed and you get a cyberzombie with some mental issues, fail and you get nothing. Interestingly, I seem to remember that a glitch lead to a seemingly successful result but something went horribly wrong, and on a critical glitch the zombie would go into a homicidal rage and kill everything in sight.
Rough details:
The Invoked Memory Stimulator is mostly like a flashback device; when triggered it would flood the subject with powerful emotions and memories, essentially keeping the metahuman part of the cyberzombie anchored to the near-dead body.
Essence; I don't remember any limits, but the ritual gets prohibitively more difficult the more Essence is lost so that's sort of a limit in and of itself.
Significant lifestyle cost increase (duh; it's expensive as heck to keep one of these things alive

)
Astral Hazing (Force 4, should be able to use the rules from 5th directly)
Monthly Willpower+Intuition (1) test to avoid losing their mind; failure essentially means you get more and more negative qualities or loose attribute points
Dual Natured, I think with a Magic attribute of 1
Attribute boosts; each full point of Essence below zero is added to attribute ratings (maximums, I think, not current)
Immunity to normal weapons; double negative Essence, so a zombie with -6 Essence would have 12 hardened armor for example. This might need to be adjusted for SR5 where AV is much higher
I'd have to reference the book to make sure I didn't miss anything, but I think those are the highlights. Ultimately, though, you can make it whatever you want; as long as the creature has negative Essence, a shit-ton of augs, and undergoes (and survives) a rare and challenging ritual performed while the difficult and expensive surgeries are performed, you should be good. Unless this is happening to one of your players, in which case; good luck
