We have developed LACE, a fast and flexible modular DNA assembly method that is scalable up to chromosome-scale. LACE is intended to reduce the barrier to entry to synthetic genomics, making it easier, faster, cheaper and accessible to a wider range of researchers. Unlike existing techniques that rely on expensive and inflexible large DNA fragments, our starting material is individual genes or functional elements. These can then be assembled rapidly to a predetermined design or combinatorially, with genes in any desired orientation and with the option of stock or custom features such as recombination systems. Unlike previous methods where redesigns require resynthesis or in vivo genome editing, our method is able to reuse the same parts for any number of design variants and is compatible with existing Mo-Clo formatted parts collections. This allows both iterative redesigns and parallel assembly of many prototype chromosomes. Whilst the method uses Saccharomyces cerevisiae as an assembly host, we envisage that it will used as a general method for synthetic chromosome assembly for a wide range of host microbes. We plan to release LACE as a freely available kit that will enable researchers to assemble synthetic chromosomes for their own applications in a timescale of weeks.