I used a pine timber 8 3/8'' x 8 3/8'' x 24 feet long from a sawmill near my house... it only cost me 70$/Can ... one year later, the wood was enough dryed to have alot of fun and project for that price :-)

Step 1: Cutting and Rough Sanding

At this stage, the best preparation for determining the lengths of the 2 post (vertical and horizontal) is to draw the desired result on a scale drawing. That way, you wont come up with bad proportion. For my need, I chose 68'' for the vertical and 48'' for the one horizontal.

The circular saw didn't cut enough deep to go thru the entire beam ... I needed to use my saw-all to finish it. (a chainsaw would have do the job easily)

Finaly, I sanded all faces with 80 grit to make it easier for tinting later on ...

Step 2: Joining Cut-out

Trace the desire location of the cut-out on both pieces. Since the cut-out need to be haft way of the timber (4 3/16'' deep), I used my 8'' dia. circular saw to make aroud 20 passes ... The more cutting you do, the easier it will be after to remove it with wood chisel. But still, I was only at 2.5'' depth ... Then, I use (1 cut on 3) my saw all to go at the desire depth. If you're more patient than me, I would recommend to do it on each cut ... :-) ...

After that, it's time for wood chiseling ... You dont need to make it perfect ... but be sure you're at the desired depth everywhere in the cut-out plane and dont forget to let a little gap (about 1/8'') to make it possible to join them together.

Step 3: Assembly of the 2 Posts

I would lie to you if I told you that everything fit right away. After a dryfit, I had to lightly sand one of the openings. Even if I had planned to put iron angles in each corners, I glued everything together. That way, it was easier to manipulate the assembly for further process.

Step 4: Chamfer

This is a personal choice ... (only aesthetic) ... I made 1.5''x45° chamfer at each end ot the top ends. (Not the one at the bottom). I've done that with my circular saw ... It came out nicely even with poor precision (not using guide). I would recommend to make it on a table saw (with guides) before the assembly was done ... I also did 1/4'' chamfer everywhere else with my sander.

Step 5: Address Frame

I used 2x4 and and a 3/4'' laminated pine board ... According to your sketch dimensions, start by cutting your 2x4 frame at 45° each end. Next, using a table saw, I grooved a 3/4'' x 3/4'' cut-out in the middle of each 2x4. (required for panel insertion)

Next, assemble and glued everything together. (I used small nail gun)

The result was pretty neat and cheap ... Nicely done Simon :-D

Step 6: Tinting

It's time to tint everything ... since it will stand outside ... make sure to use good product for exterior purpose ...

I've done 2 layers as recommend by the supplier.

Step 7: Hardware

From the beginning, I planned to put iron angles on both parts (post and address frame). I bought pre-drilled big angle (4'' x 4'' x 6'' lg.) for the post and smaller one (2.5'' x 2.5'' x 3'' lg.) for the address frame. I put the angle on interior for the post and installed them on the exterior for the address frame.

I painted the angle in black. (paint designed for outside weather)

It always good to predrill the wood when it's time to use lagbolt .

And finally, screwed the address numbers on the pine board.

Step 8: Mounting Plate for Concrete

You can imagine that the overall project is heavy ... So it need to be well grounded ... To do so, I have designed a plate that would have 4 exterior legs and 4 clamping screws ... I used (4x) 1/2'' threaded bar (about 24'' in long) with each end bended. (it will act as reinforcement in concrete) And I used (4x) 1/2'' x 6'' lag bolt to secure the plate in the post ... (You'll need to drill 4 holes in the post to accept the threaded head bolt).

Sadly, I dont have any photo when I've done my concrete setup ... I dug a wide and deep hole enough to accomodate the reinforcement in the ground ... I stabilized the address post (with rope and everything that can help) at is right place over the hole ... And only after all was in place, I prepared and poured the concrete (I used about 10 bags of concrete for my slab) ... DONE DEAL !