Following these steps will work whether you are building LWB, CLWB, MWB or SWB. Very tall riders will need to use shallow head angles and lots of fork offset (rake) to get an LWB with good steering ergonomics and a comfortable seat recline. Conversely, shorter riders may need steep head angles and a 16" front wheel to design an optimum SWB.
2. Start by drawing these items in place, then determine where your shoulder joint will be.
3. Reach; Draw an arc centered on your shoulder joint, with a radius 2" less than the distance between your shoulder joint and your wrist. You hands should end up somewhere along this arc. If your reach is too short, there will be little or no self-centering action, If it is too far, your hands will tire, and you will have trouble making the larger steering corrections needed at low speeds without letting go with one hand.
4. Determine how far the center of your handlebar grips need to be from your BB, to allow the desired clearance between knees and hands or bars.
5. Swing an arc centered on the BB using the above distance. (I use 28", I'm a typically proportioned 5' 10" but I like my bars low. So I let the knees come up between my hands to about the thumbs. See http://bikesmithdesign.com/EvoBars/EvoBarSetup.html ) Where this arc intersects the first, should be the center of your handlebar grips.
6. Decide how much tiller you want. 8" seems about optimum, but it's hard to get that much on an SWB without a pretty steep head angle. With an LWB and a fairly laid back seat you will end up with a really shallow head angle if you try for 8" but with the right bars 10 or 11 is OK. Shallow head angles are fine if you can add enough rake to keep the trail under 1/2".
7. Draw an arc ahead of the center of your grips, with the tiller as the radius.
8. Then decide front tire diameter and crank length and whether you will be LWB, MWB or SWB. Draw the front tire as close to the BB as possible without having crank/tire (or fender) interference. A properly designed LWB will not have much wheel behind the steering axis, so from a side view can have quite a bit of tire/crank overlap without the cranks actually hitting the tire. Most of my cranks overlap the fork and headtube, without hitting the tire.
9. From a point on the ground, 1/2" ahead of the center of the tire's contact patch, draw a line tangent to the arc centered on the hand grips. This line represents your steering axis (headtube). Measure the angle between this line and the ground to get head angle.
10. Draw a line perpendicular to the steering axis from the front axle. The length of this line is your fork offset (rake).
11. Wheelbase; Locate the rear wheel of an LWB or MWB such that you end up with about 1/3 of the weight on the front wheel. Much less and low speed balance will be a bit of a chore. Because the CG was further ahead of the rear wheel, my old 66" WB bent was easier to balance, and therefore more maneuverable, than my new 59" WB one.
12. Orient your handgrips as shown in http://bikesmithdesign.com/EvoBars/EvoBarSetup.html The downward bend of the bars shown here is vital to opptimize control. However the exact angle is not important. I like about 58 degrees, for max control and comfort, but knee/handlebar overlap doesn't bother me. Even a 40 degree downward bend is a huge improvement over nearly straight bars, and usually doesn't cause knee/bar overlap.
Do a little experimenting, changing rider position. You will see how all these factors, especially seat height and tilt, affect head angle. Also see what effect raising the hands a few inches has on head angle and/or tiller.
Note that I'm not telling you how to design your frame. I don't care if you are using titanium or resin-impregnated corn flakes. If you use this method to determine the location of the axels, handgrips and steering axis, based on the riders position, you will end up with a sweet handling 'bent.