Abstract
Despite advances in indoor scene generation, synthesizing coherent building exteriors consistent with generated interiors remains largely unexplored. Existing methods can generate floor plans and wall layouts but typically stop at a structural shell, lacking stylistically consistent facades and roofs. Completing these exteriors is challenging because the footprint, wall geometry, and opening semantics must remain fixed—constraints that unconstrained generative models often violate. We introduce ShellMaker, a language-guided exterior completion framework that operates under these structural constraints. Given a building scaffold and a text style prompt, ShellMaker generates a complete exterior mesh with PBR materials by combining parametric roof generation, LLM-based part-aware prompt refinement, joint wall–roof material retrieval, and geometry-aware assembly. Operating on a format-agnostic scaffold representation, ShellMaker generalizes to indoor generators, CityGML, and CAD inputs, while maintaining structural consistency and improving architectural coherence over retrieval and unconstrained generative baselines.
Qualitative Results
(Top) Two input scaffolds each rendered under two style prompts, demonstrating preservation of wall geometry and opening placements across variants. (Bottom) Nine additional styles applied to various scaffolds, illustrating the breadth of architectural styles ShellMaker can automatically generate with appropriate roof forms, materials, and detailing.
Comparison
Given the same scaffold and style prompt, generative baselines often produce visually plausible exteriors but fail to faithfully preserve the scaffold footprint, exhibiting incorrect aspect ratios, omitted footprint boundaries, or geometry extending beyond the scaffold. Methods that better respect the footprint frequently do so at the cost of degraded texture quality. In contrast, ShellMaker preserves the scaffold geometry while producing stylistically consistent exteriors. Red circles highlight subtle footprint mismatches, objects outside the scaffold, and incorrect structural semantics.
Urban Block-Scale Generation
ShellMaker can be applied independently to multiple buildings to synthesize coherent streetscapes. (top) Raw building scaffolds produced by the Holodeck indoor scene generator, showing interior layouts and structural shells. (bottom) Exterior meshes generated by ShellMaker from the same scaffolds, with roofs, materials, and facade details added while preserving the original building footprints.
BibTeX
@misc{xu2026shellmakerlanguageguidedexteriorcompletion,
title={ShellMaker: Language-Guided Exterior Completion under Structural Constraints},
author={Ruiqi Xu and Daniel Aliaga},
year={2026},
eprint={2606.31680},
archivePrefix={arXiv},
primaryClass={cs.CV},
url={https://arxiv.org/abs/2606.31680},
}