Phew, I misread. You are already having the house extended upwards! But this ditch around your property needs to be filled in, otherwise you've actually built a water fortress.
Morning,
The front part of the property is also being filled by about 40 cm.
You have to imagine, there's a street at the property, on my side without a sidewalk, only with a 5 m wide grass strip, which is city land; this grass area is about 15-20 cm lower than the street.
I would roughly assume this height; you can't just fill in the city's land.
Because of that, I would still be about 15-20 cm lower than the street level on the property; the house itself is still higher, about 17 cm higher than the street.
I know it's a bit much, but maybe now it's understandable. I just can't imagine there would be problems with rainwater.