Make a (somewhat) self-referential string

C, 64 bytes

l,i;main(n){for(scanf("%d%n",&n,&l);i<n;)printf("%0*d",l,i+=l);}

Takes a single integer as input on stdin.

JavaScript (ES6), 83 bytes

n=>[...Array(n/(l=`${n}`.length))].map((_,i)=>`${+`1e${l}`+l*++i}`.slice(1)).join``

Yes, that's a nested template string. 79 bytes in ES7:

n=>[...Array(n/(l=`${n}`.length))].map((_,i)=>`${10**l+l*++i}`.slice(1)).join``

Jelly, 12 bytes

VRUmLDUz0ZFU

I/O is in form of digit arrays. Try it online! or verify all test cases.

How it works

VRUmLDUz0ZFU  Main link. Argument: A (digit array)

V             Eval; turn the digits in A into an integer n.
 R            Range; yield [1, ..., n].
  U           Upend; reverse to yield [n, ..., 1].
    L         Yield the length (l) of A.
   m          Modular; keep every l-th integer in A.
     D        Decimal; convert each kept integer into the array of its digits.
      U       Upend; reverse the digits of each integer.
       z0     Zip/transpose with fill value 0.
         Z    Zip again.
              This right-pads all digit arrays with zeroes.
          F   Flatten the resulting 2D array.
           U  Upend/reverse it.