Do I say "Jsi vysoká?" if I'm asking a female here then?
Is (vysoky) considered to be related to masculine word as (vysoka) is considered to singular feminine ?
I do not understand your question. Vysoký is the masculine form, vysoká is the feminine form and vysoké is the neuter form of the same adjective.
Are you big is not accepted?
No, vysoký - tall, velký - big.
Sometimes there is some overlap, but in this case only on the Czech side. We do accept velký in the reverse translation.