Depreciation question when paid less then land value for house/land.

[Kevin Macdonald]

I am reading a book “every landlords tax deduction guide”, which was recommended to me from this site. I understand that the 27.5 year depreciation is only for the house and not the land value.
I bought a piece of property where the house was constructed but never finished. I am in the process of finishing the property and use it as a rental. These are not my numbers but I will use as an example:
Land tax appraised value from state records 300k not including any structures on land.

Purchase price of land and half constructed home 200k.

Rehab cost to complete project and get it ready for rental 100k.
How would I break up my original 200k purchase into what part is considered towards land and what is considered part of the existing house which was not completed? Do I have to consider the whole 200k towards the land since the land is valued at 300k?

Even though I paid less for land can I still deduct my rehab costs (100k)?

thanks