Hello Martha,

First, is it approved to raise chickens where you live?  Some housing developments and towns/cities have restrictions.  

Oregon State has some nice publications for backyard chicken coop design: https://extension.oregonstate.edu/pub/ec-1644  This should help with predator  proofing, sizing, and other things related to the needs of the chickens.

There are many sources of plans depending on size and how fancy you wish to make the coop.  This is a link to some free Extension based plans.  There are many options based on size.   Although many of the plans date back many years, this includes some plans for smaller coops and might help with getting you started: https://www.ag.ndsu.edu/extension-aben/buildingplans/poultry

Most feed supply stores will carry a variety of feed.  If you start with layers, there are usually a couple options of "layer feed".  Some will be crumbles and some pellets.  What your chickens prefer may depend on what they were used to getting when you purchased them.  Either type should provide the appropriate nutrition.  If you are getting them as chicks you will want to put them on a starter grower feed first and switch them to a layer feed latter.