Having your own building constructed, whether it's for personal or commercial purposes, can be both an exciting and stressful project.  Though you will need to manage every aspect of the build yourself, that control is a benefit.  You can create a space that's exactly suited to your needs.  Granted, it's a little more complicated than simply collating your ideas, and you will need to rely on the expertise of design and construction professionals.  However, there are some things you can decide on your own - and, indeed, you should decide on them in advance of your meeting with any designers or architects. Here are a few places to start.

Budget

It doesn't need to be specific, but the very first thing any designer will need to know is approximately how much you're able to spend.  No decisions can be made on sizes, materials or essentially anything else before this is established.  By the same token, it may also be helpful to have a timeline in mind - but be prepared to be flexible with this in accordance with what the experts suggest.

Functional Requirements

If you know you need a certain amount of storage space and a specific number of offices, then you should outline this in a list for your designer.  Everything else can be built around these base requirements; finer details such as layouts and lighting can be left to the designer.  If appropriate, you could also consider prioritising your wish list so that the designer knows which elements are most needed, and which can be shrunk or removed in order to accommodate the rest of the design.

Aesthetic Preferences

If you do have an idea of how you'd like the building to look, then it's helpful to let the designer know about this in the early stages.  After all, there's no use having them design a traditional office space if you'd prefer something sparse, spacious and modern.  Equally, if you are a fan of specific materials or colours, then it's always worth making a note of these.

Having your building designed and constructed will be a long and drawn-out process with lots of opportunities to add information and make changes - but that's no reason not to get this first meeting off on the right foot.  Giving your building designer all this information in the first instance will give them some great blocks to start with, and ensure you at least begin with a first draft that's workable - whether some changes are required or not.