I would recommend a classic.
Total Annihilation. If you can get the original game from Cavedog, then add a mod called "Units Compilation Pack" or "UCP". Affectionately known as "TA:UCP". It is a good mod, there are many others but this is popular.
If you try, because it is an old game and Cavedog is no more, you may be able to find a couple copies for free.
It was the LAN game of choice for years over here. Very fun. Basically you and your friend would play as a team against the AI, and you can have more then one AI team, who even fight each other as well as you.
Check it out.