Would be trying to get a trap so the outlet would be as high up as possible. About 10mm mortar bed I would hope. Just wondering if I will have enough fall from the raised shower tray to the drain which goes in to an outside gulley at floor level. About 2 meters away.
It always exits quite high. You normally have to cut a hole in the ply just to get the trap up close to the tray. Two metres should be fine. 4" = approx. 100 mm so you have up to 50mm per metre which is plenty.
The minimum falls are a bit misleading . In real world situations things can be altered and work fine - if you got a shallow seal trap and put a cleaning eye on your pipe where it exits the wall you could have a small fall, clear water will get away fine it's when the soap deposits build up that you need the cleaning eye and a snake And do put the waste pipe below the gulley grid or you'll end up with a rancid grid I think the official fall is 2.5 degrees