The mast is going to be hollow box-section and the boom is going to be a solid rectangular section. Here is the cross-section of the mast from the plans.
The boom is about 9 feet long and the mast is about 18 feet long (just a few inches shorter than the garage). The lumber I purchased is only 12 feet long, so I need to scarf together pieces for the mast.
The pic below shows all the douglas fir pieces of the mast and boom cutout and ready to be glued together. The pieces on the right are for the boom. The longer pieces on the left are for the mast. An important detail to notice is that all of the scarf joints are staggered, so that they will not be all in one spot of the mast. This makes the mast stronger. (Also shown in the middle of the pic are some oak pieces that will be the rub rail along the shear line of the boat ... not related to the spars.)
I've also started making the mast step. The mast step is where the base of the mast rests on the boat. There can be large forces traveling through this joint, so it need to be built stout.
The mast step in the plans doesn't seem quite strong enough to me, so I've decided to beef it up a little. Here is a pic showing the side of my mast step (left) compared to the one shown in the plans (right). I'm also going to secure everything with big screws and lots of epoxy.
Here is a pic of the mast step during the initial dry fit, just before gluing.