"I am very tall."
Translation:Ich bin sehr groß.
"Groß" is rarely used as "fat". There are some euphemisms like "große Größen", or "große Mode" when shops advertise size of XXL+, but this is more than polite. They just use the standard word for "tall" in a different context as a "code" for big sizes, but including also normal proportions, so, things for people who are just very tall, not fat. That's the only usage of "groß" as "fat" which I can think about.....