Hi Dean,
Thanks for your question, I think it is going to be of interest to some of our other users

To select your own start point just click it in the drawing window during the Ceiling Grid process instead of hitting <Enter> or your right mouse button to accept the 'Middle of Room' default value. The prompt at this point is 'Select the start point for the T-Bar to be calculated/<Middle of room>:' .
So it is easy to use a specific point instead of letting DraftLogic Electrical make a determination of room center for the starting point of the ceiling grid pattern. We're all good so far if you are content to select a start point this way. If you are not content, the trick is giving yourself a concretely determined point to select other than having to 'select by zen' with nothing to guide you other than eyeballing and instinct.
The first thing to be aware of is that most layers are turned off for the Ceiling Grid tool in order to reduce clutter and give you the best chance of selecting the polyline you want. So you'll need to place any guide points or guide lines on a layer that will stay on, like the room boundary layer (zDL_ROOM_BDRY).
The second thing to be aware of is that the point you select is going to be the intersection of four grid cells. So if you want something other than the intersection of four grids to occur at your target point, you actually need to lay down guide lines or a guide point that is offset. For example, if I am putting in a 2'x4' grid but want the cell center to start at the room center that I have selected, I would put down a couple of lines 2' and then 1' away from the point I want the cell center to start it. It is this offset point that I will select as my grid starting point.

- WithStartPointGuidelinesAndOrPoints_20101211.png (6.27 KiB) Viewed 18339 times
If I want to try out a variety of start points and see how they fit the room, I will set up my reference points options and then copy the room boundary & reference points to an open area of the drawing.

- CopiesReadyToMakeGridOptions_20101211.png (3.49 KiB) Viewed 18339 times
Then I will take the few seconds to fill them all with grid using the Ceiling Grid tool & decide which one I want to actually use.

- GridOptions_20101211.png (9.95 KiB) Viewed 18339 times
Once I have decided, I can do a crossing select and shift de-select to ensure I select only the ceiling grid lines and not the room boundary and reference lines but then use a corner of the room as the base point of the move (same for start and destination to line up the move nicely).

- SelectedAllThenDeselectedNonCeilingGridLines_20101211.png (7.05 KiB) Viewed 18339 times

- MovedSelectedGridToRoomToKeep_20101211.png (11.42 KiB) Viewed 18339 times
As always, feel free to call, email, post to forums, or Skype chat if you have any questions about this or any other DraftLogic Electrical matters!