TL;DR
Increase Roboport sprite size slightly.What ?
The Roboport looks like it doesn't occupy its top-most tile. I'd like to suggest increasing the size of the Roboport sprite slightly.I think it would also benefit from being larger horizontally, so that it fully occupies its left and right-most tiles.
Why ?
After 400 hours in the game, I still find myself underestimating the true size of the Roboport sometimes, thinking I have an extra free tile when I don't.Here is a screenshot illustrating the issue. As the oil refinery and chemical plant slightly extend past their tile box, it looks like the Roboport should do the same, but in actuality it occupies an extra row of tiles at the top.
This is perhaps not worth changing right now, as it might be too disruptive a change, but I'd like to suggest it for the upcoming DLC.
P.S. Feel free to move this to the Bug Reports forum if you think it's better suited.