Hm? I dont quite get what you mean. Do you mean laying more then one grass at a time?

I don't know much about isometrics(if thats a word) but here's a demo:

http://developer.byond.com/hub/Shadowdarke/IsometricDemo

I'll just cover the case where your iso icons are 64x32, you're on your own to figure out how to display them otherwise.

If they aren't going to be /turfs, you'll need to dynamically create each "turf" as an /obj. Basically you read turfs off of your map and then calculate how they should be displayed on your "display map". This guide is for starting at the top left of your map and moving right, then moving down a row etc. As each row gets drawn, you find that the turfs will look to be going top-left to bottom right. Here are some points:

1. Every turf on an even-numbered x turf will need to be shifted down by 16.
2.
a. For each even numbered row of turfs, shift the current y down one tile if the turf's y is even
b. For each odd numbred row of turfs, shift the current y down a tile every two turfs

3. Always move the current x one tile over for each iso tile that gets drawn.

4.
a. For each row of turfs, always move your starting x left one
b. For each row of turfs, move your starting y position down a tile for each even numbered row of turfs.

Starting x and starting y are where you *start* drawing a row of iso tiles.

Current x and y are the x and y for each individual iso turf.

Phew. I hope that makes even the least bit of sense to anyone. :p One thing might be to get a piece of paper, draw a bunch of blocks and try to see how isometric icons would fit into BYOND's tile grid. That should also give you an idea of how they should be drawn. There used to be an excellent article(along with other stuff on all manners of isometic games) on setpixel.com about it, but that site is gone. :|