women's dress (Khartoum)

Greetings Khartoum folks!!

Please could someone explain what is considered appropriate dress for a foreign woman.

Covering shoulders - but should be down to where? Is a normal T shirt okay or down to elbow or cover elbows or down to wrists? If worn with trousers, what about the length of a shirt/blouse - does this have to loosely cover down to what level? Mid thigh? Are jeans permitted if you wear a tunic style top? Are loose trousers more acceptable than loose skirts or the other way round? Where should the skirt of trousers come down to?

What is a public area with respect to dress code? Does this include your room in a hotel? Are you allowed to be with a tank top and shorts in your room or is this shocking? If you have a garden at home, is this public (because someone could look in from the street?) If you have a guard or people working at your house?

Also, from what age do girls need to cover up?

Thanks for any enlightenment!

Mari