Provided with a strict set of rules a computer program can perform the role of a simple designer. Taking advantage of a computer’s processing power, it can also provide an unlimited number of variations in the form while following a given set of constraints. This paper delineates a model for interrelating a rule-based system based on purely architectural considerations with non-deterministic computational procedures in order to provide controlled variations and constrained unpredictability. The experimental model consists of a verisimilar architectural problem, the design of a residential tower with a strict program of 200 units of different types in a given site. Following the interpretation of the program, a set of rules is defined by considering architectural concerns such as lighting, dimensions, circulations, etc. These rules are then encoded in a program that generates form in an unsupervised manner by means of a stochastic search algorithm. Once the program generates a design it’s evaluated, and the parameters on the constraints are adjusted in order to produce a new design. This paper presents a description of the architectural problem and of the rule building process, images and descriptions of three different towers produced, and the code for the stochastic-search algorithm used for generating the form. The succesful evolution of the experiments show how in a computation-oriented design process the interpretation of the problem and the rule setting process play a major role in the production of meaningful form, outlining the shifting role of human designers from form-makers to rule-builders in a computation-oriented design endeavour.