First mistake: thinking about the garden when it is too late.
The garden is an essential complement to the house and a multiplier of property value.
Designing the house and garden together allows you to manage an overall budget and make more functional choices.
Thinking about the garden only at the end of the construction work is definitely too late: many choices will be conditioned and we will probably have exhausted the available budget.
So: think about the garden as an investment and design it together with the house, since they are two complementary parts of a single reality, our home.