Guess there’s a sting in the tail here, possibly connected to the need to a) extend the house, b) drain the cess tank; c) have access to the roof; d) any other activity connected to the house rathwer than the garden, which makes the wilderness option the likely alternative … which would/might (hedging my bets, here) be a shame. So …

Guess you need to get a mini-JCB in and flatten a part of the wilderness, get an experienced pond-designer in (you have two, well one, at least amongst your friends … moi) and go for the “up-the-hill” option with lots of tunnels and viaducts.