There are actually 2 of us mappers that are currently working on campaigns. They are:
-Aro who is working on
Twisted Insurrection which has had a mini-release. It is more of a mini-mod with a campaign as its focus IMO.
-Then there is me, Ixith, and I am working on
TS: Covert Operations which will feature missions that aren't really connected to each other by one bigger story. Rather they will have their own separate mission story which may or may not relate to other missions.
Also there were 2 campaigns made awhile back by Spy005 called "CABAL's Revenge" and "The Never Ending War" Both require firestorm if I remember correctly. You can probably find them if you searched for them.
I am sure you can look at either place and check out basic mission ideas. Though it really depends on how you want your campaign to be if you are indeed making one.
A few ideas would be:
-make sure if you set up an overall story that it is either a nice addition to the already established TS or FS story or can be seen as a plausible side thing between the two factions.
-When creating a mission plan out how you want the mission to play out and what kind of objectives you want to use.
-Keep your missions varied. Don't just have all the missions' main objective be "destroy all units" add spice and have some missions that involve destroying a single structure, unit, or bridge or have it be to capture something.
-Use side specialty type things as a nice touch to maps. In other words have a GDI mission in which requires you to stragetically control an amphibious assault. For Nod use subterranean vehicles or cyborgs.
-Have some missions have that "screwed from the get go" type feeling. In other words have missions where you start out with only a few units of some kind and need to escape or find a new base or help a small civilian village from something.
I hope those suggestions give you some basic ideas. I would really like to see another campaign come out. So good luck and happy mapping!