IO for the number of permissible full floors

Hello I have a question about the development plan. What does the IO mean in permissible full stories? And at the bottom right, does that mean only gable roofs are allowed?

The "usage template" should be explained in the plan legend. "I" for the floors makes sense here, but "o" for "open" I do not know capitalized and also not as if it were virtually "one word" with "I". Where the "^" is, the roof shape indication would not be unusual, but without an explanation it would be too vague for me.

but "o" for "open" I don't know capitalized

In the Eifel, they don't take that so seriously.

without explanation

There is also one in the legend: sloped roof at least 25°

thank you.

i.e.
detached residential house,
the ground area may be a maximum of 200 square meters
gable roof with at least 25°
then unfortunately I do not understand the number of full floors and the maximum height.

Single-family detached house

Correct.

The footprint may be a maximum of 200 square meters

Correct, if the plot is 500m² in size.

Gable roof with at least 25°

A gable roof is not mandatory, the main thing is that it is at least 25° pitched, so also shed roof, tent roof, hip roof, truncated hip roof.

then I unfortunately do not understand the number of full floors

What exactly do you not understand?

the maximum height

I have found nothing that restricts this.

What exactly do you not understand?

Probably the single-story aspect or that single-story refers to a full story and not to roof extensions/so-called half stories.