Bike travel bags, hard cases, and homemade bags
If you travel regularly, buy a decent, high quality hard shell or accept your bike will be damaged. Even with the very best case, your bike could be damaged - either accept it as a cost of travel, or purchase travel insurance that covers the bike. 

Depending on your travel and carriers, you will probably find a home made case will offer poorer protection and cost more in baggage charges due to it being heavier. Its unlikely a home build case can be made light and strong compared to a commercial hard shell.

Also consider the cost of a damaged bike is may be far more than the cost of repairs. If you bike is badly damaged going to your destination, your entire holiday could be ruined. Travel insurance can help here as you would not need to be concerned about cost of repairs at destination (e.g. say you bend a derailleur and the only available replacement at the bike shop is Ultegra or XTR, insurance would cover the repair cost).