Rob has got the BritModeller (BM) Group Build (GB) formula right. As he said there are over 10,000 members over there with a few hundred (or more) actively participating in GBs. That is why their calendar is so full and the Bunfight (or vote) happens this time each year to determine the following year's schedule.
It works well over there. ARC used to be a big GB forum as well but GB interest has waned over there. They recently had an F-14 GB that was successful, but the site seems to centre around Teen Series Fighters and modern US hardware so that is why I think it went so well, the first in quite a few years.
The Unofficial Airfix Modeller's Forum (UAMF) is another I frequent, they have another GB methodology. Like BM you need to suggest a topic and take ownership and if it gets up moderate the GB. The thing is with the moderation you can have more than one, BM GBs usually have 2 mods to help run them. Anyway UAMF have a smaller GB participation rate and you may only get a few interested, I think 6 is the minimum required for a GB to start. Someone suggests a topic, enough interest is garnered, the GB overlord agrees it has enough support and then the group decide on a start date. UAMF GBs are usually short, 4-6 weeks while BM GBs with go for 2-3 months. I think there is a bit of work for the GB Overlord in those forums, moderating and monitoring the chat about future GBs, approving them, creating new forum sub sections for each GB and then allocating permissions to the moderators to be able to edit and remove GB posts as required. I have moderated a couple of GBs over at BM and it is not too onerous, just need to keep peoples build rate and enthusiasm going by commenting of their threads and motivating to get back to it if a thread is not updated in a while. Here is a link to a BM [img=https://www.britmodeller.com/forums/index.php?/forum/616-boeing-737-stgb/]B737 GB[/img] I moderated back in 2018, we had 35 builds started and 21 completed.
As Rob also says those other forum sites cover all modelling subjects, we are a little shoe horned here but I think if we do allow the subject matter in GB to diverse I think it may work. I am not sure what others here have interests in to suggest other topics, cars, ships, spacecraft???... military aircraft of course!
With the possible demise of AMI perhaps we could coax some of those folk over here, expand the forum a little to allow for subject creep and would have more folk for GBs as well. I am sure this has been in others mind's as well.
So I am in favour, I suggest the UAMF model be used and tweaked as required. Both Forums mentioned have the GB sub forums and chat area where there GBs are suggested and support gained. I think initially this should be advertised/mentioned in the general chat forum or perhaps,
Here is a link to the
UAFM GB Guidelines, they are quite extensive and set out well.
BritModeller's GB guidelines are not as concise but here is a link to their
GB FAQs section