If you want a larger scale RTS then Rome might not be what you want. It's a great game (the original, that is - Rome 2 is only 'good' by my judgement) and it does have RTS battles, but they aren't really the same as SCII. There is a much more chaotic and jumbled feel to the combat compared to the chess-like SCII.

I don't know if it's on sale, but I would recommend Supreme Commander if what you want is large-scale RTS (or Planetary Annihilation if scale is all that matters.) It, along with its expansion Forged Alliance, have good single-player campaigns and a really massive scale; in the original, the build time for a tech-II tank from a high-end and engineer-supported tech-III factory was a few seconds, whilst the base build-time for submarine equipped with nuclear missiles was something along the lines of 300 minutes (which you would reduce by assigning engineers to assist the build, which consumed resources faster and so required a larger economy. Balancing that was a big part of the game.) 

If you want a larger scale RTS then Rome might not be what you want. It's a great game (the original, that is - Rome 2 is only 'good' by my judgement) and it does have RTS battles, but they aren't really the same as SCII. There is a much more chaotic and jumbled feel to the combat compared to the chess-like SCII.

 

I don't know if it's on sale, but I would recommend Supreme Commander if what you want is large-scale RTS (or Planetary Annihilation if scale is all that matters.) It, along with its expansion Forged Alliance, have good single-player campaigns and a really massive scale; in the original, the build time for a tech-II tank from a high-end and engineer-supported tech-III factory was a few seconds, whilst the base build-time for submarine equipped with nuclear missiles was something along the lines of 300 minutes (which you would reduce by assigning engineers to assist the build, which consumed resources faster and so required a larger economy. Balancing that was a big part of the game.) 

Does supreme commander have a good vs ai mode or anything? I think I heard about it before but, idr why I lost interest.