1) a wood shed is a good place to practice, it is small and perfection isn't as essential. So it's a good place to make your first scarf. Better here I'd say than on a house or somewhere, where a mistake would be disastrous!
4),5) the quality of your pegs depends a lot on how you raise your frame, and how the various timbers interact with each other. with braces, the joints are always supposed to be in compression, and there are a number of historic examples of braces being pegged with twigs, just there to hold them together until the frame is up in which case it should hold itself together.
If you have a simple mortise and tenon tie joint, than it is in tension and the peg is very important.
Some historic frames, especially in Continental Europe, may not have a single peg in the entire frame!
6) around here, that is the way it was done on about all barns. The rafters and joists are generally 2x (true 2x, not 1 1/2 stuff you get nowadays) and the rafters are birdsmouthed and spiked in place with gigantic spikes, like a modern polebarn spike.
the disadvantage of this, in our barns the rafters were often staggered at the purlin, with a different rafter for the top section and the lower section. As a result, you can see the purlins from the outside of about every barn around, the roofs have sagged and the purlins have heaved upward. The purlins in this style of roof have more upward force than the downward force exerted by the rafters, and so the result is a net upward force which shows up after 100 years or so... This combined with the tendency of 2x rafters to sag significantly over time causes the roofs to be very wavy.
DLB
