FAQ:
Q: I want to have more storage space.
A: You don't need storage space. Spend metal immediately. Stored metal sacrifices tempo for versatility. You need to know the intricacies of most unit interactions to use that versatility and even then you still need specific situation to use that. As a rule of thumb, don't store metal.
Q: I understand but still want storage (because I'm a pro or don't care about optimal play).
A: Make the storage building.
Q: But I want to have storage on Commander.
A: Use your Commander to build the storage building.
Q: But what if my base dies?
A: Protect your base better.
Q: I couldn't, I got 2v1 and couldn't get help!
A: Hide your storage.
Q: I tried the above and still lost my storage.
A: Make a new one.
Q: But that way I still lose my stored metal!
A: Not if you make the new one before the old one dies.
Q: I can't always predict my old storage dying.
A: Only in extreme cases. For the extreme cases the enemy has to be super sneaky and for that he deserves to remove your stored metal.
Q: I still think it's good to have an insurance against losing my stored metal.
A: It is extremely suboptimal. If you accept that, make redundant storages.
Q: But good player XYZ makes tons of storages!
A: Yes, but they actually do have that much metal, it is not stored metal loss insurance.