Why does it say "v'Kam me'Al Mishkavo va'Yis'halech Al ha'Gag"?
Malbim: When David ate by himself, he slept until nine hours. When he ate a royal meal, he slept until evening 1 (Yerushalmi Brachos 1:5, Midrash). Today he rose at evening, i.e. he had eaten a royal meal with delicacies. And when he rose, he did not engage in public needs; he merely strolled on the roof; therefore, he came to sin.
I did not see anyone cite such a text! Our text in Eichah Rabah 2:22 says that when he ate by himself, (the meal ended three hours before evening; he slept until four hours into the night, and rose to engage in Torah). When he ate a royal meal, it ended at evening, and he would rise at midnight to engage in Torah. Also the Yerushalmi says that he rose at these times, but it did not say when his meals ended. (PF)
What was "me'Al ha'Gag"?
Radak: David was on the roof when he saw her bathing in her house. Malbim - even though from the roof he needed to intend (direct his glance) to see her, when he saw her, he did not turn away.