Inheritance Insights

I'll be inheriting money along with my 4 siblings (great affection among all of us, multiple million dollars each) in the next 2-10 years, as my parent is 78 years old. I want to build a garage to make my house feel like a forever home. One estimate for demo and a modest rebuild was $100k. Should I start saving now (10+ year plan) or get a plan in place to use the inheritance money ASAP? I (and the 78-year-old) feel like the market will drop soon along with around half of the inheritance. What are some possible market scenarios and best practices to maximize my inheritance? Will build prices drop, or is this just the new normal? Thank you very much. Huge fan of your podcasts and kudos to your cohosts for not burning up in your magnificent humility.