Advice needed for bi-fold doors

[mandm65]

Guys I am hoping to install bi-fold doors for our new extension. We are planning to have the opening to be around 4.5 meter wide.
Can anyone highlight the pros and cons of the idea and perhaps what type of door (UPVC, Aluminium, wood) I should look for? I have seen in the pics where doors are flushed rather than step over but unsure if it can be problematic during heavy rain etc?
Cheers

 

[God]

Ali bi folds all day and standard threshold, get use to stepping over it, with a low thresh you will have problems with it sealing in rain and wind

 

[mandm65]

Thanks mate unsure if i could decrypt Ali bi folds
Right you have a valid point re sealing in rain/wind i thought the bottom of the door runs on some sort of track so does that not help with sealing?
Cheers