When used with a form of sum, the gerundive — which is passive — denotes necessity or obligation, as in the phrase dē gustibus nīn est disputandum. A passive periphrastic construction merely points to existence of a need or obligation.
Omnia haec facienda sunt. (All these things have to be done.)
Since gerundives are passive, there is no need to say whose problem it is. If you do want to make a reference to the person who needs to attend to the matter, you use the case that shows interest in something — the dative.
Omnia haec tibi facienda sunt.
(All these things have to be done by you.)
A better translation would be “You have to do all these things.” That translation, however, is blunt and loses the indirect, beating-around-the-bush flavor of the original Latin. The Latin actually says something more akin to “As for you, all these things need to be done. (And just what are you going to do about it, eh?)”
This use of the dative case is called the dative of agent.
Some Latin gerundives have made their way into everyday English. The neuter plural of the gerundive of agō, for example, is agenda, “things which must be done.” Another good example is memorandum, “a thing that must be remembered.”