If I have a family I'll build a house big enough for my family to live in. / But if I don't have one I would like to renovate the house I live in with my mother to make it more modern without having to be too fancy.
If I had a family, I would build a house big enough for my family to live in. I can decorate the house where my mother and I live more modern, without needing to be too luxurious.
If I have a family, I will build a house big enough for my family to take care of it. But if I don't, I will transform the house where my mother and I live into a more modern one without being too extravagant.