East Midlands Trains Sundays inside roster at Derby:
10 week repeating pattern of rest days.
Gives 1 in 2 Saturdays off and 1 in 2 Sundays off. These are always together as a long weekend of 4 or 5 days grouped together. The other rest days are usually a minimum of 3, but there is one occasion of 2 which is the one week where only two rest days occur. The missing rest day that week is given back the following week. This gives a better 'weekends off' situation than 3 rest days every week. You'd need to use +/-1 annual leave day if you had an annual leave week on one of those weeks.
Sometimes in this roster the shift change from AMs to PMs and vice versa occurs midweek at the rest days. This slows down the body clock change required, but might meet resistance as some prefer shift change to occur at at the weekend which makes things difficult when a Sunday becomes a 'rest day' and a minimum amount of 32 hours rest becomes a requirement.
South West Trains Farnham roster:
Rest Day pattern repeats every 8 weeks. Has 1in2* Saturdays off and 5in8 Sundays off.
*However, the last few lines don't quite fit the pattern so as to accommodate additional Saturday turns.
London Overground New Cross Gate I believe:
A staggered week of rest days Thursday to Wednesday every 4 weeks. Mostly every other weekend off although the pattern alters near the bottom to accommodate weekend work. Random single rest days for the remainder.
There are also (It isn't a good picture I'm afraid) several weeks of the same shift sometimes put together (3 or 4 weeks of mornings for example).
Personally, I like the Derby one as it is a repeating pattern and every weekend (1in2) is a long weekend of a minimum of 4 days. This is better than the 2 out of 3 Saturdays they were working before when they had Sundays outside the working week, and finishing late on Saturday and starting early on Monday with a Sunday off inbetween with which they couldn't do much!
I would get a "maximum of 50% weekends worked" included in your negotiations if you can. Chiltern (who currently have Sundays outside the working week) have a "50% of Saturdays must be rest days" clause, and London Overground (Sundays inside) have a "maximum 26 Sundays rostered per year clause". London Overground originally had 19 per year written into their conditions and got a big pay rise and a reduction from an average 4.25 to 4 day week keeping the same average turn length (separate to a good multi-year deal) to go to 26. If they hadn't had a figure to be rostered per year they wouldn't have got anything extra at all!
Are your membership to expect working 19 Sundays out of 30, like LNER at Edinburgh, or could they have more weekends off initially but then have them taken away over the years with no negotiation. This has become an issue at London Underground.
So get a figure on weekend work in your negotiations is what I'd recommend. Then they'll know what to expect and have safeguards in place.