About the theme this should be a RTS on the lines of games like AOE3 and SC2 because those have proven to be the most popular ones. Games like Civilization or Total War have a completely different style.
In my opinion go for a combination of these: The 2nd one from age of empires is definitely the best hud layout i have seen in a strategy game. Mostly because of all the slots that allow for developers to focus on building a library of improvements with different button icons rather that more complicated inventory like huds . The other two are more detailed, very cool designs from dota2 for huds. So i say grab the design from the dota2 ones and mix it with the HUD from AOE3.
http://hydra-media.cursecdn.com/dota2.gamepedia.com/1/14/MLG_Stronghold_16x9.
http://img145.imageshack.us/img145/2721/aoedota2.
http://hydra-media.cursecdn.com/dota2.gamepedia.com/e/e5/Alliance_HUD_16x9.
A quickmockUP
For the HUD raster based with these ratios 21:9, 16:9, 16:10 , 4:3 ( I think the resolution should be the same for all of them just different aspect ratios[For example: 1980x1080p for all of them , the difference will not be noticed.])