Can I use a car's sunroof as a sukkah? Taking my Subaru Forrester as an example to get some approximate numbers: it has a sunroof of approximately 30 inches by 30 inches. This exceeds all opinions of what constitutes 7 x 7 tephachim.
The sunroof is a few inches from the windshield and from the doors. Am I right that I am covered by Dofen Akumah?
Is the slant in the windshield a problem or prevent it from being a wall? I don't think this is a problem but I am just checking.
Based on your description, you have 3 Kosher walls, which is sufficient - and maybe 4 - depending on how large your windshield is; up to 4 Amos you are allowed a דופן עקומה. (You may want to check the statusof the back window also).
You also have the required 7x7 tefachim.
The only missing info is the height - you need 10 Tefachim of useable height on an area of 7x7. Since your car seats are solidly attached to the floor (I hope), I don't think you could start measuring from underneath the seats.
See the Aruch Hashulchan 633:10 who says:
ולכן סוכה אין החלל שלה גבוה עשרה טפחים – פסולה. ואפילו היא גבוה עשרה טפחים, והסכך הוא למעלה מעשרה, אלא שהוצין יורדין לתוך עשרה – גם כן פסולה, ואפילו הם חמתה מרובה מצילתה, דאין הפסול מטעם הסכך אלא משום דלא נשאר עשרה טפחים אויר לתשמיש, ואינה דירת אדם.
