There's a few things that need to be addressed.
First you need to 'define' a procedure that will accept the arguments (the SF-OPTION, SF-IMAGE, etc) that are specified in your 'script-fu-register' call. This procedure should have the same name as the first argument to 'script-fu-register' ("TMETurboBrand").
Second, it is not necessary to specify SF-IMAGE and SF-DRAWABLE because your script is creating them, rather than using pre-existing ones.
Third, your use of 'gimp-image-new' is correct, however, the image created does not have any layers yet (so 'gimp-image-get-active-layer' will fail). You need to use 'gimp-layer-new' and 'gimp-image-insert-layer' to add a new layer to your image.
The following code addresses the first two issues; I leave it to you to address the third.
(script-fu-register "TMETurboBrand"
"<Toolbox>/Xtns/Script-Fu/TMEturboBrand"
"turbobrand"
"azimuthcgi"
"JL Clifford"
"april 2014"
""
SF-OPTION "SF-OPTION" '("STL" "Bar" "Square" "Highboy" "Executive Tower")
)
(define (TMETurboBrand option)
(if (= option 0)
(let* (
(thisImage (car (gimp-image-new 1024 469 0)))
(thisLayer (car (gimp-image-get-active-layer thisImage)))
)
(gimp-display-new thisImage)
()
)
(if (= option 1)
(let* (
(thisImage (car (gimp-image-new 1024 657 0)))
(thisLayer (car (gimp-image-get-active-layer thisImage)))
)
(gimp-display-new thisImage)
)
(if (= option 2)
(let* (
(thisImage (car (gimp-image-new 1024 657 0)))
(thisLayer (car (gimp-image-get-active-layer thisImage)))
)
(gimp-display-new thisImage)
)
(if (= option 3)
(let* (
(thisImage (car (gimp-image-new 1024 657 0)))
(thisLayer (car (gimp-image-get-active-layer thisImage)))
)
(gimp-display-new thisImage)
)
(if (= option 4)
(let* (
(thisImage (car (gimp-image-new 1024 657 0)))
(thisLayer (car (gimp-image-get-active-layer thisImage)))
)
(gimp-display-new thisImage)
)
(gimp-message "Please pick an item")
))))))