Custom fences are actually relatively easy to create. Fences do not do recolors, so the only way to make a fence recolor is to clone it and change the texture. We also have the ability to make them BaseGame compatible, so let's do that!

SimPE:
Start up SimPE in Advanced Mode. This is in your Preferences and after you tick the box you need to close SimPE and open it again for it to actually be in Advanced Mode. Then start Object Workshop. Fences are in Other. Find the one you want to work from and click Next. You should really consider choosing a fence that is from any EP. BaseGame fences have wonky lod90s (the way you'd see your fence in the neighborhood view). They also have screwed up bumpmaps. Bumpmaps do not work on fences at all, so don't bother with it. Pick a nice EP fence that kinda looks like what you are making and clone from there. It should also help you with your meshing.

To create a 'recolor' tick the box 'Reference Original Mesh'. If you are making an entirely new fence mesh, don't do that. Click 'Start' or 'Next' to continue. Give your new fence a name and a price. Then click Finish.

Register GUID
Now the GUID is where things are slightly different. You need to make sure you are using a GUID that isn't conflicting with another fence, but fences don't seem to mind sharing numbers with objects. You need to use one of your GUID numbers for this. You can use a brand new number or reuse a number you've previously used for an object (recommended). While previous tutorials have said its ok to just pick a random number and hope it doesn't conflict, but that's just bad practice. It is your job as the creator to make sure you don't infringe on anyone else, so use one of your numbers.

Mesh and Texture:
Go ahead and mesh up your fence as you would any other object. There are some good tutorials here -> http://www.modthesims.info/forumdisplay.php?f=541

BaseGame Compatibility:
After that all is done. Save your fence. Then click on the 'Resource Actions' tab (if you can't see it, select the Resourse Actions entry in the Window menu; if still you can't see it, reset the layout of SimPE from the preferences). Click the 'Fix Fence' button and hit 'Yes' on the warning that pops up. This will make your fence BaseGame compatible.

Catalog Placement:
If you want to change where your fence appears in the catalog, open the Text List in the created package, and you will find three rows of Text. The first one is the Title, the second one is the Description, and the third one is the Priority (0-Based) in the Catalog. Fences in the Catalog are sorted by increasing Priority, meaning first the Fence with Priority 0, then 1... Two fences can have the same priority, but you cannot tell the game which one comes first in that case. So if you set your custom Fence to 1, and there already is a Fence with Priority 1, the item will still be one of the first in the List.

Fence Posts
As for the fence posts, you can change whether or not the fence puts down posts at every tile, or just where you start and stop dragging. Open the XFNC resource and change the vertical post frequency in the 'posttilespacing' line.

Save your package again and try out your fence!

Further Resources:
Modding Info Center Partitions: walls, fences, fence arches, Fence Arch Info Thread, Fence Post Info Thread, My question thread, SimPE Site Fence Tutorial

Hi Phae, I was making another fence and I really wanted the posts to override some other fences posts. What exactly are we supposed to put in the third string of the textlists? Every time I clone a fence there s no 3rd string....

Edit to add. Scratch that, I think it makes no difference for what I wanted. What it seems to be is that if fence A has a post every tile and Fence B does not, then when you combine the two fences together you will get a post on every instance of fence A. Which is slightly annoying with this combo I am working with

The third line in the text list is actually the price. This is what shows in catalog as well as the cost to the lot. The cost line in the xfnc appears to do nothing. At least in a multiple EP game config.

Thanks for this tutorial, it's really helping. However, I can't seem to find the 'posttilespacing' line anywhere.

Hello LadyAngel!
The line "posttilespacing" not present in all fences.
For example: the gray stone fence no has post, the red brick fence yes has post.

Ah, I didn't realise that. I'm using the white, picket fence, which does have a post, so I'm a bit confused (not that it takes much!).

Forgive my stupid question, but I don't see where to make a GUID on a fence. I'm trying to recolor the Schifting Partition, but all I see when cloned are Fence DML, Material Definition, Resource Node, Shape, Text Lists, and Texture Image. SimPE 0.73.44.37511

There's a line inthe XML called 'guid (dtUInteger)'. Put your GUID there. You can re-use a GUID you have assigned to an object before, but don't use GUIDs from fences, walls, stairs, or doors.

If you go to Resource Actions there is a line for Fix Fence. This randomizes the values and makes the fence base game and it will not have the cc star. Otherwise you can place a hashed value in as the GUID, or recycle one from an object since they do not conflict. Doing this, the fence will have the cc star.

Awesome, both of you! It's been a while since I toyed with meshes.

I've been messing around with it a little bit, converting a privacy fence from TS3.
I tried cloning from a basegame fence and it turned out to be pretty straightforward actually, assuming you don't mind hacking around in the .package file a bit.
You'll basically have to delete anything that resource with a name that contains lod90 and then make sure you delete it from the lod listing too in the remaining SHPE resource as well.

As a sidenote, when I click 'fix fence' in SimPE the warning says something about TS2 University, are custom fences without 'fix fence' applied just not supported before that expansion?

IIRC, University was the only EP out at the time "EP-ready" options were added to SimPE, so that warning was probably never changed. Having the base game and any EP will make fences work without making them base game compatible, though you will obviously need the specific EP containing any non-base game fence that you want to clone. The lod90 resources are what make your fence visible in neighborhood view. They are usually low-res versions of your texture and pointers to the gmdc via shpe.

Good to know, I thought cloning from a basegame fence might make it basegame compatible as well, but I couldn't test it with AnyGameStarter since I have the UC and it will always have M&G installed.
The lod90 would allow you to provide your own mesh and textures for neighborhood view, but the game will generate neighborhood meshes for you if you remove all references to the lod90.

I believe using the 'Fix Fence' option will make it base game. It also will remove the cc * from the fence. But as d4RE mentioned, any EP works, not just Uni. I don't recall that cloning fences pulled the lod's, hrm. Typically I point the lod's to use the mesh/textures I've created anyway.

I cloned an EP fence before and it didn't have them, it only pulled the lod meshes when I cloned a basegame fence out of curiosity.
I assume Maxis got lazy/smart and decided to not make neighborhood lods after the basegame and instead left it up to the game to generate textured planes, which pretty much gives you the same visual result at the default camera distance.