Deferment is an important concept in design. Escaping from a strict hierarchy of inflexible decision-making can be important both in the quality of the result and in avoiding decision reversals and rework during design and construction. Engaged in a speculative activity, the designer never has access to all the information influencing any particular design decision. The object of design, whether building, artifact, art piece, film or computer game, as the confluence of many decisions and influences is intrinsically both complex and incomplete during the process. This paper will examine a detailed example of a way of structuring a digital design model geometrically to maximize its flexibility and the opportunity to tune geometrical decisions late, in the light of as many different factors as possible. Paradoxically, this example employs a rigidly hierarchical system of organization employing a tree structure that avoids lateral links and "evolutionary dead ends" in order to work effectively. Thus one rigid hierarchy of decision making at meta-design level replaces another to achieve deferment and flexibility at formal design level. In architecture, the opportunity to defer or suspend precise dimensions and relationships by substituting for these with parametric relationships has proven advantages for collaboration. These manifest as unparalleled precision in construction, time- and cost- savings at the production end of the process. At a more conceptual level, parametric modeling also provides the opportunity to experiment geometrically at comparatively little cost in terms of rework. The current work in progress on the upper colonnade of the west transept of Antoni Gaudf's Sagrada Fanulia church begins to introduce a new level of interest into the parametric tree, an opportunity through equation driven parametric relationships to generate form not only through defined geometric relationships but to introduce variable finite and infinite series into these relationships.