It is not necessary to use a Windstorm Engineer for most repair or construction projects. The Texas Department if Insurance (TDI) maintains offices and inspectors throughout the coastal areas subject to hurricane force winds where windstorm inspections are required. These inspectors will perform the necessary inspections to enable you to obtain windstorm certification for your repairs or construction free of charge. They will do an excellent job and will make certain all work is performed to current code requirements. The reason there are paid engineers who perform similar services is that the TDI inspectors are very busy and may not be able to schedule a site visit as quickly as needed.
TDI inspectors do not do planning or design work so if you need these services, or if timing is important, you may need to use the services of a windstorm engineer. If you determine this to be the best course for you, I recommend getting the engineer involved as soon as possible. Having an engineer involved from the start of a project can help eliminate mistakes in the early process that can be expensive to correct later in the project. The engineer should work with you and your contractor to make certain that all work is done to current code as modified by TDI and to be sure that a windstorm certificate will be issued upon completion of the project.
Many contractors have engineers they know and are comfortable working with and will make providing a windstorm certificate a part of the construction process. I think it is a good idea to have the name and contact information for the engineer being used in the project if you have not contracted with them directly. The TDI maintains a list of their Approved Qualified Inspectors on their website. Check your contractors engineer to verify that they are on the approved list. Hiring your own engineer, on the other hand, guarantees the engineer is working directly for you and has your best interests in mind.