Some of the things you will have to be concerned with include a 2" drain for the shower, at least 3" for the toilet, 1-1/2" for the vanity. All drains must be vented* and have at least 1/4" per foot slope. The toilet flange sets on top of the finished floor andthe center of the flange is located 12" from the finished wall behind the toilet.
*Toilets that are 6" or less from the main stack do not have to have a separate vent.
This should give you something to start with.