"Je ne suis pas grand."

Translation: I am not tall.

[cskeranen]

I am not big doesn't work?!

[CommeuneTexane]

Grand(e) refers to height in humans, and gros(se) to weight or girth.
Elle est grande. = She is tall.

However, grand(e) can also mean "great" if it precedes the noun.
C'est une grande femme. = She is a great woman.

[Sitesurf]

C'est un grand homme = He is a great man

She is a great woman = C'est une grande dame, c'est une femme remarquable

C'est une grande femme = She is a tall woman