What is wrong with this angle?
Hex infill patterns are normally chosen for strength, as the honeycomb resists force in many directions. However, hex infill patterns are slow to print and the older, simpler fill patterns print faster and provide sufficient support for solid architectural models.

Models with shallow roof angles of less than 45 degrees are challenging to print and often result in "air prints" where unsupported filament cascades into a sorry tangle of sadness. Shallow roofs are challenging because each horizontal filament overlaps very little with the preceding adjacent filament. This is where infill proves critical, since the infill supports these filament bridges as they cross each infill line segment.

Slicing software has only recently introduced the hex fill pattern because the code to print a hex infill is VERY complicated. You can see this in the picture as all those fine lines of retracted filament scattered throughout the hex infill. Earlier, simpler fills such as diagonal lines provide simpler longer paths for the slicer to implement. Bridging works best at speed over many supporting points. Excessive retraction causes the extruder to "stutter", and makes bridging difficult.

It may therefore help to choose a simpler fill pattern for printing this model and reserve hex infill for simpler models requiring utmost strength.