Building a blockchain could look like not a complex task, but the evil is in the details.

You can roll out something  looking like a working blockchain in a month or so, but many questions appear before real production launch:

1. whats the algorithm - PoS, PoW?
2. if PoW, what's it - sha256, cryptonote, egalitarian algorithms, ASIC friendly or not?
3. if PoS what kind of - DPoS, NXT-like, PBFT (Tendermint), Algorand, etc?
4. whats the money  supply?
5. if PoS, how to distribute - give to Bitcoin holders, Ethereum holders, give to random people by captcha, give to Bitcointalk members by rank, give for investors only on ICO, how many to keep to yourself?
6. whats the format of address, is it possible to use passphrase, is it digits only to simplify use for enter, whats with control sum to prevent error during input?
7. wallets - mobile version, desktop version, should it be cross-platform, what framework to use if so (qt has quite not really modern L&F, Atom is slow, Java is memory hungry)

...

345. Probably we better go with a fork?