Getting max level heroes is a lot of work. And it also takes a lot of time. To make matters worse, raiding without a hero can be rough and warring without a hero is very ill advised. Well I can't fix any of these issues, but here is a simple guide on how I am able to upgrade a hero every week while only missing out on one war each upgrade. Be forewarned, this method will cost you about 450 gems (or just under $5) per upgrade after hero down time caps at 7 days per upgrade.
To completely gem a hero for a full 7 days cost 1,000 gems or about $10, and by not gemming at all you could miss out of 3 wars. In comparison, a cost of $5 and 1 missed war may sound more reasonable. Not to mention the benefit of having your hero back half a week early for raiding.
Lets assume you already have enough dark elixir to upgrade your hero and that it takes 7d per upgrade. In order for this to work, one must only ever start their hero upgrade within the first couple hours after war begins and you can make both your attacks. The sooner you make both attacks, the sooner you can begin the upgrade, and the more gems you will save. After making both attacks, opt out of the next war. At some point after the following war begins (that you opted out of), opt back in so you will be in the next war. If you are following me, then you will have only missed 1 war. When the next war starts, you just wait to make both attacks until the final 12 hours of that war. And that's it. The longer you wait the more gems you will save, but make sure to give yourself time to make both attacks and fully cook both armies. Boosting your barracks or gemming an army to attack in time would kind of defeat the purpose wouldn't it?
Day 1 - War 1 begins and you make both war attacks ASAP. Have both armies ready to go if you can. This can be done within first hour of war assuming your heroes are killed, or within first 10 minutes if they aren't! Probably gonna need about an hour though...
Day 2 - War 1 ends and we start search/prep for next war . Dont forget to opt out!
Day 3 - Prep ends and War 2 starts. You still are opted out for this war. Feel free to opt in now for the next war though!
Day 4 - War 2 ends and we start search/prep for next war. You are opted in!
Day 5 - Prep ends and War 3 starts. You are in this war, but you won't be attacking until tomorrow!
Day 6 - Gem your hero complete for ~450 gems and give yourself enough time to make both attacks before war ends. War 3 ends and we start search/prep for next war. You are still opted in!
Day 7 or Day 1 - The cycle has begun anew! Prep ends and War 4 begins and you make both war attacks ASAP. Have both armies ready to go if you can. This can be done within first hour of war assuming your heroes are killed, or within first 10 minutes if they aren't! Probably gonna need about an hour though...