a. Hiring Inexperienced Architect And Designer. Building regulations for Accessory Dwelling Units (ADUs) differ in many ways from regulations for a standard single-family home. With the proliferation of ADU regulations, experts warn against hiring inexperienced designers or architects and instead emphasize the need for a professional that understands cities' specific requirements in order to ensure that everything is compliant and up to the standards. 

Generally speaking, due to its size and purpose, ADUs also allow for greater architectural flexibility than a traditional building which can be built onto or away from an existing structure in order to make the most out of limited space. While ADUs present challenges in efficient design and storage solution, here is where the expertise of an experienced ADU designer becomes highly valuable. 

An ADU designer must account the following:

1. City Regulations

2. Maximization of Space

3. Budget

4. Long-term Return on Investment

Investing wisely can lead to valuable long-term returns when properly managed by those who have experience with regulatory and design complexities associated with building Accessory Dwelling Units (ADUs).

b. Hiring Inexperienced Contractor. Hiring an inexperienced contractor can cause unforeseen setbacks, ultimately leading to delays in the project's completion. It is essential that any contractor chosen for the job be knowledgeable and skilled at the task at hand for the successful completion of the project.  

Homeowners should avoid hiring inexperienced or unlicensed contractors for ADU (Additional Dwelling Unit) construction. Before hiring a contractor, always do an extensive research to determine their track record and experience in building this type of special structure. Make sure to properly analyze the contract for reliability and accuracy of its terms. Also, review any waivers of warranty or liability that may be included with the deal. Additionally, check references from past clients to ensure that the contractor meets high standards of quality when it comes to project completion, communication and attention to detail. 

Hiring a contractor who is experienced in ADU projects not only provides more assurance of success but also ensures that the process will go more smoothly and quickly by avoiding any issues related to inexperience. Preferably, a contractor must possess the following:

Knowledge on City RegulationsComplete Team of Professionals who are also Knowledgeable in ADUFully Insured And BondedExperience building an ADU in your ciity

c. Thinking You Can Do It Yourself. Constructing an ADU is no small feat, and it isn't a job just anyone can take on. Standards and specific regulations must be followed, health hazards evaluated, wires installed correctly—all while factoring in plumbing issues as well. Not to mention essential work such as gas fitting or electrical works that require certified personnel. To ensure everything goes smoothly and safely, don’t underestimate the value of hiring a professional expert who possesses knowledge far beyond that of a DIYer; you may end up spending more upfront but will save time and money down the road.

d. Not Separating The Utility Meters. When constructing an ADU, it's wise to invest in a separate utility meter. Doing so pays off in the long run - tenants will be able independently pay their own bills and enjoy greater independence! You’ll also save yourself time and stress down the road by allowing each tenant to cover their own bills, instead of having them funnel through you.

e. Underestimating The Project Cost. When it comes to garage conversions, cutting corners isn't an option. Any quality garage conversion project is not going to be cheap. Also, miscellaneous expenses can add up and without the right budget in place, a project could remain unfinished for years on end.

Homeowners often face the unpleasant surprise of discovering that their project costs much more than initially estimated. These unpleasant surprises could be due to mold or pest infestation among others. Unfortunately these unwelcome guests might add additional costs to the project that weren't anticipated.

The initial estimate is only an educated guess based on the initial property check, and even after consulting with an architect or contractor there can still be a gap between this number and what you ultimately pay for your dream conversion. It's always wise to factor in at least 20-25% beyond the predicted cost if working from an estimation – consider it insurance against those unplanned expenses. 

It's also important to know the difference between an estimate and a quotation. Estimates can give you insight as to what your total cost could be for any given project, but quotations are legally binding commitments indicating exactly how much will be charged in the end.