towers during construction.

if the enemy builds towers, can I attack her to take over, do I have to wait until it is built?

u can attack and destroy the tower before it is built 'prevent it ’ 

I was hoping for a takeover, but ok, the question is still so - why do you need 200k of skulls when attacking towers, right at the fortress of the enemy, and they need only 4k?

Those numbers aren’t fixed, it depends on number of players participating in wars and their troop count. 

we are 2 we have 400 branches. their 6 are less than 1200. it is 7k so 2k. we lose the whole. we still need 50k, and they are only 6k.
how to understand these wars?