We find that beyond the direct cost, the logistics of getting hundreds of people to a remote site is a significant challenge for construction companies. We directly saw how much of a hurdle this can be when we were on a site with the closest city an hour and a half away. Weather conditions are also a factor here, work on the site was actually shut down due to conditions that were too cold for laborers.
As we've interviewed solar construction companies, all of them have told us that they're turning down potential jobs just because they don't have enough people/capacity to build them. Unfortunately they can't simply raise their hourly rate by a few dollars to make this problem go away, because the challenges are more the regional specificity and logistical challenges of getting workers to sites.
(For home use, I worry about my neighborhood becoming a superfund site in event of a fire. I read claims that fire burning the house under CdTe panels will not release the 8g/m^2 of cadmium on them, but don't know how to evaluate that.)
TLDR Worker housing and logistics vs robotics.
Fortunately the labor needs are typically predictable, with each step you mentioned happening in parallel across a site spanning 100's or 1000's of acres. One of the main reasons that larger sites are particularly appealing for us is that the work done by our robots is continuously in demand somewhere, as opposed to a small site which might move in more discrete stages and have the rapidly changing needs you mentioned.
Maybe 10-15% of total cost depending on install type.