Campus buildings constructed prior to 1917 represent a variety of Gothic, Classical, and Victorian architectural styles. In 1917, the Colorado General Assembly supported increasing CU-Boulder enrollment from 1,200 to 3,000 students. As a result, the Board of Regents directed President Livingston Farrand to hire an architectural firm to conduct development planning in order to improve the campus appearance.

The Philadelphia firm of Day and Klauder was commissioned to do the work under the direction of George W. Norlin, who had become the interim university president. Day and Klauder had earned a strong reputation by designing buildings for Princeton University and Wellesley College in the collegiate gothic style. Architect Charles Z. Klauder's first sketches for Boulder campus buildings were in this style represented by the existing Macky Auditorium, but he ultimately rejected them for a variety of reasons. He wanted to create a unique style that would use the locally quarried sandstone to produce architecture that would blend more harmoniously with Boulder's magnificent mountain backdrop. As it turned out, Norlin (then fully-appointed university president) and the Board of Regents agreed.

The Board of Regents approved the resultant 1919 Campus Development Plan and accompanying scale model. The model, now on display at the Heritage Center in Old Main, depicts demolition of many of the previous buildings, new symmetrically designed buildings, refinement of a quadrangle plan, axial alignments between major buildings, and additional buildings in monastic-like clusters. Most buildings shown are narrow to accommodate natural light and airflow, often with wings radiating from a central core.

Hillside villages and rural farmhouses that he had observed as an architect touring the Tuscany area in Italy, and similar styles in Spain, influenced the architectural style that Klauder had in mind. His reinvention of a Mediterranean style for the Boulder campus includes charming building elevations, often with towers and chimneys near the ends that add a picturesque quality to the cascading roofs. Sprawling wings form intimate courts that can be used as outdoor rooms for classes or retreats. The Italian influence is echoed as well by stone details, such as limestone arches framing entrances and windows, carved limestone cartouches, benches, column capitals, and fountains. Many consider Sewall Hall, completed in 1934, to be the best of Klauder's CU work.

When viewed in aggregate, the campus is reminiscent of hill towns around Florence and Siena.

Architectural historians categorize the style as Tuscan vernacular. Klauder simply referred to it as "University of Colorado Style." It is characterized by multi-hued sandstone walls and tile roofs, off-white limestone trim, and black metal accents. Exterior walls built of locally quarried sandstone vary in color from light buff to reddish purple. These split rectangular stones were laid flat face down with the fractured face jutting out from the mortar wall line, creating an ever-changing shadow pattern on the wall. The limestone-trimmed windows, doorways, and ornamentation contrast with the sandstone walls to create an overall red and white look. Roofs have various heights, pitches, and forms, complementing the stone walls and nestling well below the view of the Flatirons mountain backdrop. Roofing material is clay barrel tiles of various hues, combining to create a red or terra cotta appearance.

Dr. Norlin characterized Klauder's buildings as a physical body complementing the academic soul and spirit of the university. Remarkably, the central ideas of the 1919 Campus Development Plan, notably its distinctive architecture and variety of open spaces, have endured.