If you want to stay true to its style then over exaggerate everything. The body and roof have a ton of curve in the picture and very little in your model.
I think that this is finish, is there anything more that i can fix? (Unity) I have made texture for the roof, that is better quality than the earlier one.
That's because it's a 2048 texture reduced to something smaller than 512, especially considering all the detail from the normal map are tiny things such as roof tiling.