Our first baby was coming and suddenly I remembered that I love woodworking... I didn't need much more inspiration than that. It was a fun project from which I learned a lot. (I will do my best to explain the whole process in english. Sorry if I make some mistakes or doesn't use the proper terms)

Supplies

My last project was created using mostly hand tools, with the exception of a borrowed sander and a drill. But this time I had a new toy:

A B&D Matrix (it was a present from my wife): The matrix does not have the power to work on hard woods, but I used Ariata and Yellow Pine, so it was good enough.
An oscillating power tool (borrowed)
A drill support stand
A dowel guide
Clamps
A lot of glue
Hand tools (screwdriver, hammer, saw, etc).

Note: as I have difficulty cutting large boards or lumber, I get them sized in my local retailer store.

Step 1: Design

I like to make a design using SketchUp before I start doing any crafting project. Usually, the design is modify during the process as I take some decisions or find problems with the original design. The skp document below shows the final result with the correct proportions. This crib was designed to fit a 70 x 130 cm mattress (27.5 x 51 inches).

Cuna.skp
Download View in 3D

Step 2: Creating the Static Frame

The "static frame" is the back frame attached to two of the four legs of the crib. It will have no mobility and is probably the most important section of my design as it will hold a lot of the weight. (There are 8 pictures in this section, explaining the process)

First, I made space in the legs for a dado joint (this will be used later). This cuts were made using the oscillating tool.
Using the drill stand I made holes in the upper and lower parts of the frame. First I drill half way using a 1" flat wood bit and then I drilled a little further with a 1/4" in the lower board and all the way through the upper board. Note: I hated the flat wood bit, next time I will use a forstner bit (didn't know them until the crib was done)
I used a curtain wood bar for the slats. Each one was sized and drilled in the middle of one extreme using a 1/4" bit. Finally, I putted a dowel in every slat. This process was made only on one side (the one fitting into the lower board) Note: I think that using dowels in each slat might be an overkill, but I wanted the crib to be as sturdy as possible.
In the upper board, I used the pre-drilled holes as a guide to drill into the slats and insert a dowel. Finally, the dowels standing out were cut. Note: Again, the dowels might not be necessary, but I loved the look of the dowels on the rail.
The upper and lower rails were jointed to the legs using dowels. Note: I'm not happy with this part of the design, and ended enforcing the joint with metal pieces.

Step 3: General Structure

The ends of the crib were created with a wooden frame attached in between of an upper rail and a lower rail. Then, each side was filled with a panel.

I started this part of the design by preparing the legs for a second dado joint.
Then, I created two "identical" frames and attached them in between of the legs using dowels.
An upper and lower rails were added into the dado joints. I decided to create the dado joints to hold the weight of the mattress.
Finally, the boards were cut and paint before assembling the parts.
Some testing was needed and my 33 Kg (72 pounds) dog was a good candidate. Note: Keep reading for an update about the "dog testing"

Step 4: The Decorative Panels

My wife and I painted the panels and decorated them with four animals: two for the inside and two for the outside. The animal drawings were inspired in some Pinterest ideas.
The panels were fixed with a frame as seen in the zebra's picture. I found the wooden pattern in my local store and cut it in 45º angles to create it.
Lastly, the frame the was attached using glue and enforcing it with toothpicks as dowels.

Step 5: Foldable Frame

We decided that a foldable frame was the easiest way to go, other way, picking our baby up from the crib would be difficult. We followed the same procedure that we did in the back frame:

Cut the pieces.
Make a series of 1" holes with a distance of 6 cm (2.4 inches) in between.
Make 1/4" holes in the middle of them in one side.
Assemble the frames.
Drill some holes into the 1/4" holes and insert dowels.
Cut the standing out part of the dowels.

Step 6: Details and Finishing

We want the crib to last for some years, we didn't fixed the foldable frame permanently. That way, it can be removed to use the crib as a bed. We only fixed the lower frame using removable screws. And after applying the finish, the crib was finally done and ready for our baby, until... our dog's sister came home and both decided to play over the crib; 65 Kg of jumping dogs (150 pounds) were to much to handle for the wooden crossbeam...

Step 7: Fixing the Crossbeam

We used two metal bars that a friend found in his home for the new Crossbeam. The bars were old so my wife painted them with primer.

We tested the crib again, this time with a total weight of 200 Kg (440 pounds) of People + Dog, we are sure that it will survive our baby for some time.

Step 8: Final Thoughts and More Testing

This project was a total blast. I enjoyed every second of it (yes, even the sanding). Our baby girl has already used it for 8 months and we are so proud of the final results. It's certainly not perfect, but we learned a lot about woodworking by doing it. I encourage anyone with an upcoming baby to craft something for him/her... you wont regret it.