I think what you are looking to do can be done fairly simply as shown above.
Your property would be a new Security. Name it whatever you want. Create a cash account and deposit the cash you will use to pay for it. Enter a „Buy“ with the price you pay and for „1“ share.
Then you can enter the change in valuation manually in the historical quotes tab. Having anything automated I don’t think exist, not as far as I know. In the US, there could be something like Zillow but not sure if it is worth developing anything special as this is not something that would need to be updated too often.
If you make improvement with new cash, make a new deposit in cash account and then mark that as a „fee“ for that security. Then enter the new valuation for that date as well.
It becomes a bit more difficult if you buy with a mortgage. I am trying to figure out the best way to do this so that I can reflect the regular principal and interests paid. Should I reflect only the equity or make a series of buy of some fractional number of shares every time I pay so that after the length of the mortgage I „own“ the entire 1 share? Or buy 1 shares at the beginning with a negative cash account and adding deposits to that cash account as a pay off? Not sure if this would throw off PP having a negative balance.
Not too sure of the best way yet. Trying things out.