CHMod on a dir for a particular user.

I've to allow an particular user to access a particular directory, but I've
no access to the server. The administrator said I've to create a dir by a
php script (I know) and give full access to the httpd and group, but limited
access to the particular user. (I don't know how).

Chmod only allow to change mode for proprietary, but how if I want to allow
particular things on a particular user only ? Should I use chown ?

for example, "root" must have full access to X dir, but "client" must have
only write and execute for the same dir. All must be done with a script.

Thanks all!

Cheers.

BoB