Don answered part of your question - the forces are normally unifor - so you have a continuous load across the truss top chord. If you are confident that the span from panel point to panel point is small enough to result in very low bending stresses, then you can collect the load at each panel point.

Example:

4' on center trusses
20psf Dead Load, 40psf Live Load (residential floor)
52" from panel point to panel point

4' x [20D, 40L] x 52" = 1040lbs per panel point

Now you've got a load at each panel point at the top chord, and you can do your frame analysis.

Once you've got the forces in the members, you can size your timbers.

Take the force in each member and divide it by the allowable tension or compression stress from the NDS tables. Now you have the area of your cross section and you can choose a size. There are lots of other factors to consider, and if you're not familiar, I would stick to the following:

Your members should be 2x the area you calculate above
No member should be longer than 16x its smallest dimension
No cross section should be more than a 2:1 ratio of long:short side

You will also need to connect the ends of every member properly - if you're using 1" oak dowels, count 400lbs for each one in the joint (probably conservative...I can give you the actual equation if you want it). Use 200lbs if you use 1/2" steel bolts. Make sure you have proper end and edge clearances for the pegs, though.

This is a pretty complex thing you're trying, and it sounds like this is either a ridge beam (in which case your loads will be much higher than my floor example), or you're doing a flat roof, in which case you've got a lot of calculation work ahead of you to determine - and limit - the deflection of the truss to prevent ponding and progressive collapse.

It's worth a shot, but you might want to pay to have a second set of eyes review the calculations (or do them independently) to make sure you don't miss a decimal somewhere.