Building a house—how much do I need?

Hello, and Happy New Year!

I 26F am working on my goals and one of them is to buy/build my own property this year. I mentioned buying, because I've been planning for this for the past 2 years, and I always thought that saving up a downpayment for a house and lot would be the first step. But recently my mother decided to transfer her house and lot to me. The house is very old and needs a lot of renovation. For context, it is a bungalow with 3 br/1 bath, and I was initially aiming for a 4br/2bath two-three story house.

My main question is—because I've decided to build/renovate instead of buy, how much would I need to save to get started? I had only planned to save a 500k-1M DP and pay amortization for the next 10-20 years. But now, because I'm deciding to build, do I need to save the whole lump sum of cash? Do I take out a loan?

Any advice would be appreciated! :)