I have several kids. Let me share some experiences with you:
A card board box is probably fine starting out, but your baby will out grow it.
The sleeping container should have walls high enough to prevent him/her from climbing out - this might take 9 months, but younwill want it
You NEED to remove all fluf and excess padding in your DIY "crib". Babies can suffocate on cute "fluffy" blankets
If you build a wooden crib, pay special care to the distance between vertical bars. Specifically, you want narrow slats so your baby cannot stick his/her head through it
My current child is in a portable "pack and play". They are cheap, portable, and fit in our closet. She turns 2 next month and it was a really good idea.