Here the printer’s manuscript reads had build; the 1830 typesetter emended build to built. Another possibility is that the original text read “had builded”. Although builded is archaic, it is found in the King James Bible. We have one case in the Book of Mormon text where Oliver Cowdery initially wrote builded, but then corrected it to built:
As explained under that passage, there is no evidence for builded in the original text of the Book of Mormon.
There are other cases where Oliver Cowdery initially wrote build; all of these appear to be instances of built that were miswritten:
For the first example (in 2 Nephi 5:16), 𝓞 is extant and reads built, thus showing in that case that the initial build in 𝓟 is a mistake for built and not builded. Similarly, the build here in 𝓟 for Moroni 7:1 is very likely a scribal error for built.
Summary: Accept in Moroni 7:1 the 1830 reading had built as the correct reading for the had build that Oliver Cowdery wrote in 𝓟.