There are four common ways to build an ADU: a markup general contractor, a design-build firm, a prefab/modular company, and an independent owner’s-representative project manager. They differ most in how the builder is paid and how much of the work is competitively bid — which is what ultimately drives your cost.
The four models, compared
| Model | How they’re paid | Cost pressure | Best for |
|---|---|---|---|
| Markup general contractor | Margin on every trade | Higher — markup baked in | Small, simple jobs |
| Design-build firm | One bundled fee for design + build | Convenient, but limited bidding | Buyers who want one vendor end-to-end |
| Prefab / modular | Fixed product price + site work | Low on standard units; site work varies | Standard layouts on simple sites |
| Owner’s-rep project manager | Transparent flat fee | Lower — trades competitively bid | Custom ADUs & new homes; cost control |
How to decide
- Want the lowest price on a standard unit? A prefab/modular ADU can be hard to beat — if a stock layout fits your lot and goals.
- Want one vendor to own design and build? A design-build firm is convenient, though you trade away competitive bidding on the trades.
- Building something custom and want to protect the budget? An owner’s-rep project manager competitively bids each trade and manages the build open-book — which is how Ground Rise Build targets a delivered cost up to 10% below a markup contractor’s bid.
Whichever way you lean, the smartest first move is the same: get more than one number. Bring us your best bid from any of these and we’ll show you, honestly, where we can save. See the owner’s-rep vs. GC deep dive or get a free estimate.
Compare us to your best bid.
Send the offer you’ve received — we’ll show you the savings.
Get a Free Estimate