this just uses normal snapping..it's pretty easy to do
I left open tiles on the layout, so you can try (click image to download cap)
drag a tile while holding control (in edit mode, before you run the cap), and put it in an empty spot
very easy to get it where you want it
I drew square sprites for the tiles and skewed them by half their length
so a 128x128 sprite gets a skew by 64 on the x axis
then I halved their heights
so the height would be 64 as well
then set the grid snap to that same number for both x and y
64x64
it works well and flexibly, for instance the river, top and bottom is the same sprite rotated
also in the cap if you run it is a simple control system
and the code to keep you from colliding into obstacles
and the z-order code to place the objects in front and behind each other correctly, so you can walk behind the tree and such
feel free to edit, use, etc...
EDIT: updated cap so camera moves and you can see the top of the tree