Design of the staged flare tip assembly is done by the flare tip supplier. Some senior oil and gas process or process safety engineers can scope out the requirements for the flare system in collaboration with flare tip suppliers. So can I. But you also need to know where to locate the flare assembly, and the elevation of the flare, and for this, you need software that predicts flare radiation levels at certain points of interest in your plant. And one also needs to determine ground level concentrations of flammable and/ or other toxic components in the event the flare flame is accidentally extinguished. And controlling case vent / relief loads should be identified. For this, you need software such as PHAST or Shell's FRED.
There is a fair amount of work in this to justify either (a) engaging a process and a process safety engineer within the Owner's organisation or (b) ask an engineering contractor to do all this initial workscoping for you, and look after things till this unit is installed and online. You choose. I'm in Sydney, Aus, while you are in Mexico - PEMEX perhaps ? Can you find some one closer to where you are? There may be several options for personnel in Houston ? Otherwise, you can write me at apachen01@hotmail.com to know more if you wish. I dont have the latest on these software programs. All I have with me now is an old version of Shell FRED.
To be safe, would be also good if you ran a mini HAZOP for this. The basic groundwork for any flare system is a dedicated design report on plant vent and relief loads which should also identify controlling cases - do you have this already ?