Purchase clan castle defense troops with gold or elixir

I think we should purchase defense troops with gold or elixir.
There should be another section in the clan castle to store the bought troops only for defense, apart from the donations which should be used only for attack, and for defense in case you haven't bought troops.
For example:

Dragon lvl 1 cost 100.000 gold and he stays in the castle for 1 day and protects your village
Dragon lvl 2 cost 200.000 gold
Dragon lvl 3 cost 300.000 gold
Dragon lvl 4 cost 400.000 gold

Wizard lvl 1 cost 50.000 gold
Wizard lvl 2 cost 100.000 gold
Wizart lvl 3 cost 200.000 gold

Archer lvl 1 cost 5.000 elixir and stays in the castle for 1 day!
Archer lvl 2 cost 8.000 elixir
Archer lvl 3 cost 12.000 elixir
Archer lvl 4 cost 16.000 elixir.

and so on..

Feel free to share your opinion about this idea and make your suggestions.