As far as wood is concerned, it will be your choice.
Regarding the tools, it depends a lot. If you buy rough wood, you will
need a jointer and a planer. Then a table saw will rip it to the
desired width. The table saw can also be used with jigs to cut perfect
miters. You will certainly appreciate a router to create some profiled
edges and other "decorations". If your frames are really large, maybe a
biscuit joiner will help you out. Depending on the style of your frames
maybe you will like to do some carving so here you are with future
purchases of chisels!
Unless you're planning on making hundreds of frames, you're probably
better off giving the jointing/planing part of the work to a
woodworking shop for a minimal fee. It might not be cost effective to
buy such machinery.
And I almost forgot... You will also need a few clamps. There are even
some evil spirits here who will suggest some red clamps... If they do,
let me tell you they're right! ;)