I'm looking forward to making a template soon. However I don't have any visible bald area, only diffuse thinning on top. I have to keep the hair long and combed forward to avoid showing scalp and even that barely works when any wind blows, I have to wear a hat outside. Because of the length and style that benefits me when it comes to not looking bald its also hard to see where I should draw the template. The only way I am able to clearly see the balding area is if I cut my hair length very short all around. I haven't done this in years to avoid the embarrassment, I am ready to do something about it but I don't know what to do. Would it be necessary for me to get a template made
by DiDi?, I live in NYC.

Why don't you just do it by taking & supplying measurements?
Front-to-back
Side-to-side
Temple-to-temple
Circumference
Front contour shape (A, B, C, AA, CC etc)

I don't see how that's easier in this situation. That being said it seems like it would just be best if I just cut my hair short again to make the template, it looks like sh*t anyway.

Hi, If your hair is as thin /wispy as you say, all you need to do is mist the top /crown area with water and slick the hair flat-down against the scalp....... then cut a long length of cling-film and lay it onto the head, tying it under your chin [not too tight !] --don`t pull it too tightly or it will tend to `shrink` when you eventually untie the bit under your chin and give an inaccurate size /shape.
Just add a few more layers of material and sellotape [there are plenty of Vids on `Youtube` on template-making] .. once you have it reasonably correct size [by using a marker to draw the outline of the thin/ area needing coverage on your head] and it`s sturdy enough, just untie the bit under your chin and trim the excess material off......it`s best to wait a few days and try it on again...it may have changed a bit [shrunk] so you may need to adjust it by adding on a bit more material here and there ....this way, you get to keep the hair you are presently working with.
Templates for a topper don`t have to be accurate to the nearest millimeter...you just need to give a representation of your skull -shape and an outline of the area to be covered... hope that helps and good luck with it !