Note that we have to distinguish between monoclausal and multiclausal structures. Monoclausal structures occur with:
temporal auxiliaries (haben, sein plus past participle; werden plus infinitive)
modals (modal verbs plus infinitive)
passive auxiliaries (for instance werden plus past participle)
and combinations thereof.
In monoclausal structures, the order at the end is as follows:
als das Haus gebaut3 worden2 ist1
In order to talk about order, it is useful to give each verb a rank, starting with the finite verb at rank 1. In the above example, the perfect auxiliary ist (rank 1) governs the passive auxiliary worden (rank 2), which governs the past participle gebaut (rank 3). Yet the order is exactly the opposite: 3-2-1, i.e. in monoclausal structures the order is descending.
Some additional examples:
ob man das Problem lösen3 können2 wird1
dass die Steuern gesenkt3 werden2 müssen1
However, there are also multiclausal structures, where the embedded clauses are called Infinitivkonstruktionen. These always involve zu-infinitives. The hallmark of these structures is that the lowest ranked verb, together with all its dependents, can occur in the Nachfeld (extraposed). In the following examples, I have used a vertical bar | to indicate where one clause ends and the other one starts.
seit ich begonnen2 habe1 | Deutsch zu lernen3
obwohl er versprochen2 hat1 | das Problem zu lösen3
In contrast to the auxiliaries involved in monoclausal structures, verbs allowing Infinitivkonstruktionen usually introduce some kind of lexical meaning: anfangen etc.; versprechen, befehlen, bitten etc.