1)If you are sizing inverter for equal rise/fall delay then the ration of p-mos/n-mos
depend on µ.
2) The size of complete inverter depends on load which is driven by inverter .In other
words it depends on path effort and stage effort.
3)Prorogation delay is dependent on following factors -Load/slew rate of the inverter and sizing.
4) Power dissipated is dependent on sizing of the inverter..
To get equal rise time and fall time, size the nmos and pmos inverters in the opposite ratio of their mobilities. (W/L)n/(W/L)p = (mobility)p / (mobility)n