I'm sure most of ya'll can skip this first bit, but better to post it than get questions later.
Alrighty, for this method you will need to have a UO macro called "last target". What this does is retain the last thing you targetted with your targetting cursor. You can find it here:
Another useful macro that works well in tandem with this one is called "last object":
An example would be an axe you would use for chopping a tree. When you double click an axe you are setting it to be the "last object" that you double clicked on. When you target the tree, the tree becomes the "last target" you chose as a target. So instead of having to double click axe, target tree, you assign "last object" and "last target" to two keys, say F7 and F8, and now once you have chopped the tree once you can hit F7 then F8 over and over.
These two macros are crazy useful for decorating, I would advise anyone who wants to get serious about decorating to learn to use them very comfortably, they are huge time savers.
Alrighty! You will need an interior decorator or two (I use two so I do not have to change their settings, one is up and one is down), an axe, nine goza mats, and enough pentagram/abbatoir/arcane circles to cover the area you wish to cover.
Because you will have to raise the goza mats you can only place tiles in areas where you can raise all nine in order to place the add on. Which means in a perfectly square room that is 8 x 8 you have to leave a border all the way around, and your add-on center tile floor will be 6x6. You can do what feath did and use the borders of heritage rugs or the edges of the add-ons to fill in the spaces next to the walls, or you can be lazy like me and slap some gozas down.
It is actually possible to "illusion" your way around this limitation in a perfectly square room - you can raise the single center floor add on tiles up enough to appear to be in the tile to the north and west, and this will fill up almost all of the next to the wall spaces except for the northeast and southwest corner tiles. However these tiles will block movement and it may be more trouble than it's worth.
This set of directions is for building a line of center tiles starting from the west side and moving east. It is a time saver to go in a line this way because you are only having to chop and replace three gozas at a time.
1. The fastest way to raise a block of gozas like this is *not* using last object/last target on each one, because there is a delay with moving an object after you have already moved it. The delay does not extend to other objects. So basically raise the first goza up by one, the second goza up by one...raise all 9 of them up by 1 and you can do this very quickly, then raise them all up by 1 again (all should be raised up by 2 total)
2. Place your add on, you will target the center goza mat.
3. This is where "last target" is necessary! Once you place your pentagram, the goza mat you placed on is now considered the "last target". So select down on your int dec tool, then hit your macro for "last target". Wait a second, then do it again. If you don't see the goza drop then try again (you didn't wait out the timer long enough). If for some reason it doesn't drop, check that your macro is working, redeed the pentagram and try again from step 2.
4. Chop the 8 tiles around the center tile.
5. Chop the 3 gozas that are on the backside of the direction you are heading in (in this example you're building a floor towards the east so chop the three west tiles)
6. Replace those three tiles in the direction you are building (in this example to the east)
7. Raise each of those up by 2
8. Hop off your mount, or if you don't have a mount you can use an ethy
9. Hop back on your mount (or ethy) and this will flip the goza on top of the detached center tile
10. Raise the goza twice
11. Start over at step two till you are done all the way across.
When you have gone all the way across the floor you can move south one tile, this would mean in step 5 chopping the three north goza mats and placing them south. Then you would work your way from east to west and in step 5 would chop the three east tiles and replace on the west.
If you have problems, such as a goza mat falling under a pentagram tile and remounting doesn't make it pop, you can use your int dec tool to raise the center tile a couple times till you can see the edge of the goza.
FUN THINGS YOU CAN DO:
If you have access to a lot of cash, you can make an all white floor (or whatever tokuno dye you fancy) this way by creating the pentagrams/whatever out of special woods (oak is most plentiful) then dying the addons before they are ever placed with tokuno dyes. As a border you can use pure white goza mats made from the dread spider silk cloth or bod reward cloth. Very pricey, but could be very impressive!
You can do this floor in any of the wood colors, or natural, you can make it partially see thru with arcane circles (very pricey with all the gems they take to make), the only limit is not being able to build up to a wall in custom homes unless you use the add-on border.
You can build stairs with these add-on pieces, or do a cute tabletop like Feath did, you can make little pedestals from boxes or goza mats and add-on centers...lots of things you can do. I feel like I've hardly scratched the surface of ways I can make add-ons do my decorative bidding!
NOTE: if you are in a custom home and are messing with this remember to lock down each center tile before you go into customize mode!