Let's say x= 25 and Cell A25 on the Detail Report sheet contains $L$38

Worksheets("As Built").Range(Sheets("Detail Report").Range("A" & x).Value).Offset(, -3).Value
becomes:
Worksheets("As Built").Range(Sheets("Detail Report").Range("A" & 25).Value).Offset(, -3).Value
becomes:
Worksheets("As Built").Range(Sheets("Detail Report").Range("A25").Value).Offset(, -3).Value
becomes:
Worksheets("As Built").Range("$L$38").Offset(, -3).Value
offset(,-3) means 3 cells to the left so it becomes:
Worksheets("As Built").Range("$I$38").Value