If I had my apartment robbed twice by my neighbors and they did so because of the design of the building, do I have the right to get out of my lease?

While you should speak with a landlord-tenant attorney about your situation and options in detail, from what you write, it would appear that you would have grounds to terminate your lease for violation of the "implied warranty of habitability" and/or "covenant of quiet enjoyment." As a general matter, a landlord is not liable or responsible for the criminal actions of other tenants, and those criminal actions do not justify termination of a lease.

However, that said, a landlord is obligated to provide reasonable security and to correct conditions affecting safety and security when he or she has notice of them; the landlord also may have to take action against other tenants if they are attacking, threatening, stealing from, etc. their co-tenants, once the landlord becomes aware of those actions.

If the same neighbors have robbed you twice and the landlord has not taken any action to stop or evict them; and the thefts are occuring because of a fundamental security flaw in the building which the landlord is refusing to address (like building a wall dividing the attic), that could provide grounds to terminate your lease.

However, whether or not a specific circumstance provides sufficient justification depends on the exact facts, and trying to end your tenancy when you don't have sufficient justification can result in you being liable to the landlord. Therefore, it is worthwhile to consult with an attorney in detail before taking action.

Furthermore, if the landlord did not improve security after the first incident, you may be able to sue him for your losses from the second one; and if the security vulnerability was sufficiently obvious and egregious that it should have been addressed even before the first robbery, you may be able to sue the landlord for your first theft, too--as part of the landord's obligation to provide premises whcih are "fit for their intended purpose," he or she must provide the level of security a reasonable landlord would. This is something else to discuss with an attorney--whether you can hold the landlord liable for your losses.