take out more on my mortgage for home improvements?

We’re buying our first home for $400k, but we’ve been pre-approved for a mortgage up to $800k. We have some projects in mind, like adding a bathroom to the basement and redoing the floors, and I’m considering borrowing an additional $40k for that. Here’s where I’m confused—can I choose how much I take out on the mortgage, or is it just tied to the purchase price? I’ve also heard about other loan options like 203k or home equity loans. But honestly, the rates don’t seem that much better. Does it make more sense to keep things simple with one loan? Any advice or tips on what’s the most cost-effective route would be so helpful! #firsttimehomebuyer #homerenovation #mortgagequestions