More questions and then some comments.
Are these timbers going to be planned on all four sides to true dimensions or are they going to be rough sawn stock? (Answer was all ready posted, "they will be hand planed".)
Are you going to house all joints? Using square rule joinery?
During a design phase I generally create some "General Frame Rules". These rules will help you in laying out and cutting all joints.
Such rules are:
1. All joints are laid out form the west side of the building (a gable end) except the east most bent.
2. All timbers are sized down to the next half inch in size.
3. All joints are laid out 2" off the layout face and 2" thick tenons or mortises, (with exceptions).
In designing a king post truss there are several very important things to understand.
First is the way the loads are traveling.
The king post does not sit on the bottom cord. It is wedged between two opposing rafters and is being held up by these rafters, which in turn holds up the middle of the bottom cord.
The struts hold up the rafters so that they don't sag with the weight of the roof and snow loads. Queens posts from bottom cord to rafter also hold up the rafter to prevent sag.
Knowing all this then the important joint becomes the end of the rafter (known as the rafter foot) to bottom cord connection. This is where all the load from the truss will enter and be transfered down the wall to the foundation. This joint has to be very strong and cut correctly to insure no movement.
You have asked several questions about the length of the bottom cord. As to whether or not it should "hang" over the outside wall.
These are your design decisions. If you want to have an over hang for shedding the water away from your building this is one way to do it.
If you can purchase or mill and create a longer bottom cord then this may be an option.
I'm not familiar with a top cord passing over the end of the bottom cord to create an over hang connection. This would be a tension joint and should be looked at very carefully.
Most of the ones I've seen have ended with a long tenon being pegged into a housed deep mortise on the top of the bottom cord. With the end of the bottom cord cut back to match the roof slope. But to do this you need to have your load paths reviewed and make sure you have enough "relish" to hold the rafter foot to the bottom cord.
The way it's done in Europe is to move the top cord in a little and place a secondary rafter over the top cord.
Such as this:
Using this type of system you have to be careful because the load being placed onto the bottom cord is moved back away from the end of the beam and you need to make sure this load is properly supported so that the bottom cord doesn't fail.
If you wanted to have an over hanging bottom cord to create a cornice then you could use this system and place the location of the principal rafter (top cord) foot over the wall. This would give your truss support and create an over hang. Just some ideas to help muddy the water.
If you have a drawing program in your computer and you are creating drawings there, then do a screen capture and create a jpg of the drawing. Reduce this in size and volume to fit the rules of the gallery section. Create your own galley and albums and upload the file there, then you can post the picture here.
If you are drawing by hand, scan in the drawing with a flat bed scanner and follow the procedure above.
If you don't have a scanner, take a digital picture of the drawing and follow the procedure above.
These are some ways to get drawings into your posts.
Also, email them to me using my regular email address and I can reduce them and send them back to you for posting into your gallery album, or post them for you.