Always build all the available buildings. The game gives no choices about what buildings to build, only when to build them, and to what level. The first level of a building is practically free.
Each new level up costs more than the previous one. Generally, therefore, you get more “bang for the buck” building lower levels. Therefore, your production (farms, mines) and storage (food, iron houses) should all be at the same level (or within one).
The goals of your building should be focused. There is no reason to have all buildings up the the stronghold (SH) level before you raise your SH. Quite the opposite, there are excellent reasons not to level up all your buildings.
A clear goal should be getting a Training Camp up to level 20 and researched, which lets you start turning recruits into epic and legendary heroes (though, mostly, rare heroes). To do so, you have to get your SH to 20, which also means getting your iron production up and have big storage buildings for it. Researching TC20 is a huge food sink, so you’ll need big farms and big food storage.
My general strategy advice on building:
- level your SH whenever possible.
- then build farms and mines up to SH level
- keep one TC at SH level up until 13. The others should get to 2, then 4, then 11, which are the “everyday” training levels.
- keep one Forge at SH level
- get another Forge to 5 then convert to Barracks. Level your Barracks only when it’s level limits your troop development.
- level up food and iron storage on an as-needed basis to hold iron needed for SH build (iron) or forge research (food)