I think gross is somewhere around 4.5%
It's hard to give you a good set of numbers because this all fell out of my personal home which I purchased (first home) in 2012.
I probably got caught a little bit by increased costs but what really added to the cost was personal choice to build stand alones with separate titles. I also relocated the original house on site and did major improvements such as complete double glazing, new roof and fully refinished inside and out (which I DIY'd quite a bit of).

We are "debt free" on our personal home and the new builds are valued at more than the total debt. This upcoming financial year likely to be the worst but I only need to see interest rates around 5% to be happy with my overall cashflow.

I'm personally very happy with what we have done in terms of contributing to supply and doing so in a way I think will lead to good outcomes in the long term. I think it will be a "good" investment in the long run but it's having a pretty massive impact on our lives and has been since about 2020.