To design your own house, if we are really honest costs a LOT of Money.
Been there done that 30 yrs ago.
If I had the money again, I would do just that...with the plans from a 1950's American home.
It would be just what I want, and I would stay there for a long time...or till the last yrs. :)
Ready made, well there are Pro's and Con's.
If you build your own home, be prepared to spend 30-40% for blowout costs.
A good show to watch about building is 'Grand Designs'. No one is ever on budget, but well worth the watch.
You can find a lot of wonderful homes that are pre-loved, and I would say if you have only a certain amount of money...go that way first for your start.