Negotiate price building supply store

[oswim]

Hello everyone! I am in the process of planning a construction of a vacation home in Orsa with loose materials and will eventually start requesting quotes from various building supply stores. Initially, I will be able to provide a rough estimate of how much material I need, but eventually, give a more precise one.

Here is our quite rough budget: https://docs.google.com/spreadsheets/d/1DzvPZDX2-6dgTwy4iDCc-OUThpZuY94EyEicjFCZFgM/edit?usp=sharing

Is there anything specific I should consider?
All tips are welcome!

Attaching sketches of the house just for fun