How to calculate the flight envelope and maneuvering envelope for the B727-200F?
Start with the appropriate sections in FAR part 25. The link is to the current version - you will probably collect bonus points if you dig up the version from the Sixties which was current when Boeing applied for the certification of the 727-223. Once the application is started, the rules remain relevant for that particular type - that is why Boeing redesigned the 737 several times over but kept the old name and the certification regulations that came with it. This is called Grandfather policy.

Calculate the minimum speed curve over load factor, then draw the v-n-diagram and the gust lines for 56 ft/s vertical gusts at sea level and repeat with 44 ft/s gusts at 15,000 ft, decreasing to 20.86 ft/s at 60,000 ft for the current version. Older versions used gusts of 50 or 66 ft/s from sea level to 20,000 ft, decreasing to 25 or 38 ft/s between 20,000 and 50,000 ft - the lower level is for the Sixties, the higher one for the Nineties. Note where the  minimum flight speed line will cross the maximum load factor - this is where your $\text{v}_A$ should go. Next, the limit speed in turbulent weather $\text{v}_B$ is determined by the point where the gust line will reach your maximum load factor. Cruise and dive speed are more tricky, but the limit Mach speeds are even listed in Wikipedia or on Airliners.net.

The negative side will involve some speculation unless you have been given a minimum lift coefficient - use 0.7 times the maximum clean value if you have nothing else. Use the intersection of the minimum lift line with the -1g line to continue horizontally and reduce the envelope between $\text{v}_C$ and $\text{v}_D$ from -1g to 0g, and you are done.