Oh, so the Gigagiant doesn't do that every time. Well then, you should probably lower the price a lot. It would become very difficult to upgrade Gigagiant, because you pay more than the original price every time you increase his level and it is very underpowered. I think you should lower the price to 50,000 DE or something. You should also up the stats too. The barbarian king costs 10,000 DE and does 150 DPS at level one. You could up the HP to 3,500, and increase the DPS to 350, that might be good.
For the regeneration time, you should start out with 1-2 hours, and by level 40, be at 4 hours, just an idea. I also think you should eventually make a table comparing the Gigagiants level, DPS, regeneration time, HP, and ability stats (amount of damage done and amount of giants summoned. For help, base your stats with the Barbarian King's stats, they are really balanced. Try to keep the same ratios.
Click here to view the Barbarian King article in the Clash of Clans wiki.