After raking up the dead grasses and throwing the refuse off the roof for later cleanup, there were still many small weed plants that would need to be manually pulled to fully clear the roof.
I would recommend that a hard rake be pulled through the media to loosen the roots, then separate the media from the weeds by running a regular rake back and forth over the mixture until the plant material is on top. This is virtually the only way to guarantee a weed-free environment up there and prevent competition for moisture.
The plot on the northernmost end of the roof is mostly filled by a low-growing succulent weed, which seems to be doing fine. Here's an up-close example:
Here's a view of the greenroof proper, and a picture of the cleared plot:
We wound up not planting the bluebonnet seeds because there are just too many weeds. The watering system was set up to water the northernmost plot about twice a week, which will be readjusted as needed.
Heavy items were hauled up using a metal bucket and rope, which were left on the roof.