Revit provides a Pick Lines option for various drawing commands.
Pick Lines uses an existing line as a reference and draws an identical line offsetting a specified distance from the reference line.
The following shows the use of Pick Lines to draw grid lines. The same technique can be followed for some other drawing commands.
Duplicate lines using "Pick Lines" (a quicker method after drawing the first grid line)
Left-click: Architecture or Structure > Datum - Grid > Draw - Pick Lines:
Change Offset to specify spacing between lines:
Left-click the reference grid line to fix the new line:
Move from the above of the second horizontal grid line > Left-click it to make it the new reference grid line and to fix the new grid line:
Repeat the action. All new grid lines will be 4000 mm from their own referenced grid lines: