When you buy supplies on account instead of paying cash there and then your suppliers are your creditors until you pay them. Enter in your cash flow forecast the payments you will make to your creditors (including VAT) in the months in which you will pay them. These might include technical publishers or suppliers of artists materials and computer supplies with whom you have negotiated account facilities.
Many projects need specialist input from other consultants such as quantity surveyors, landscape designers and so on. These are usually appointed by the client, who is also responsible for paying their fees, but in some cases you might be required to deal with this. Where this occurs it would be normal for credit terms of 30 days or so to be allowed.
During the course of a construction project there will be many costs that you will pay on your client's behalf - for example fees for submitting planning applications or the cost of advertising for tenders. These payments are referred to as 'disbursements'. Although your client eventually reimburses you for the cost of these items you should enter them here in the cash flow. Make sure you keep a record of disbursements and include them in your invoice to your client.