Good Day anhphuong,
Thanks for the post.
I believe this would be because of where the material is applied to the roof. If it's not applied in the same way as it it in the PlusSpec group then there's a high chance that it won't appear in the takeoff (e.g. applying the material to each face instead of the group which contains the faces). I would recommend to look at how the roof geometry has been grouped and reference the SketchUp Entity Info window to see what material & layer have been applied or assigned to each group.
What I would recommend is booking in some one on one training. If you'd like some more info on this, the link below will take you a page on our website which explain this in more detail.https://plusspec.com/buy-training/