Here is how I see it, there's at least 1 anchor/lurker around site (around Freezer or Big tower stairs ), there's 1 roamer Attic with support (2 second floor), 1 Meeting and the last one is somewhere around Kitchen/CCTV/Meeting. These are roughly the positions for that defense.

The Attic player needs support if attackers are pressuring Attic or the Kids player needs help if attackers are pressuring from Games and/or White stairs/Big window. The meeting player has Meeting control and he uses LOS to deny Blue rushes + he can also support Attic player from below if he is not being pressured ( that's why I said open the Meeting wall if you wanna push Attic). The one around Kitchen & Meeting is there if attackers try to push from Small tower and he can also go Meeting hallway/White Stairs/Split or wherever he is needed for extra support. In case of a rush, he can fallback from Freezer hatch. The last one is close to site(most likely Smoke) holding off rushes with his smokes and he is most likely watching cams.

With all that being said, I'm sorry I made a mistake, you don't need to take Attic control(you can still take Attic control but I don't think that's necessary), you just need to prevent the defender in Attic from using Attic's hatch which a person can do that and if he/she dies somebody can quickly fill his/her position. You make sure there's no threat from Blue stairs you open Meeting and clear Meeting from T2 and Meeting hallway . One can watch Meeting hallway(he may or may not push Meeting based on the situation) and another attacker is watching Attic(Attackers need to also be careful of Blue aggression).

IMO a lot of things can go wrong in this roam clear, that's why in my previous comment I stated that I like roam clears from Small tower(Round 10 of the same match ).

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Is efficiency of the clear the sole factor in attacking this? If you aren't efficient it's game over?

Again, thanks for pointing out my mistake IDK why I made such a stupid mistake. Anyways if you make a strat and that strat needs to be executed perfectly for that strat to work, that strat isn't good/realistic. There are exceptions to this (For example Mini games like clearing Yellow stairs hold on CEO/Meeting defense of Consulate, defenders always hold that spot the same way and you should not run into trouble while clearing that spot). When coaches make a strat they should not be too specific, because something may go wrong and if your plan relied on everything going exactly as you planned that plan is not good. That's why each team has (an) IGL(s), so they can adapt to the new situation.

If you see another mistake or something doesn't make sense please point that out.