DEAR SAM: I own 4 1/2 acres of land in Albermarle County, Va., now valued at $4,500. While earning almost $20,000 a year with no appreciable bank account, could I realistically hope to borrow money to build a two-bedroom house?

ANSWER: Your 4 1/2 acres, it seems to me, should be worth more than $15,000. Is this valuation taken from the assessor's records? If so, then the records have hardly been updated to today's general values of land. Undoubtedly, this large parcel could be subdivided into four lots, especially if it has the required frontage. On that basis each lot of 1.125 acres should be saleable at $10,000; however, a real estate broker or appraiser in your area should be qualified to give you an appraisal of the present fair market value.

A conventional mortgage from a federal savings and loan bank should be obtainable for at least 80 percent of the proposed house and land value; hence, with your ownership of four lots, a two-bedroom house on one of them should easily be financed.

You might consider first checking with the building department of your town to see if a land subdivision of one acre is permitted in the particular neighborhood. If it is, you should engage a surveyor to make the subdivision. Then you could sell three lots to a builder, who could build you a suitable house for the value of the lots plus some small amount to be financed by a lender.

DEAR SAM: Last summer, I discovered a large number of bubble-like ridges across the width of the tar and slag roof of my town house. The roof was resurfaced last in 1968. In 1974, the third-floor attic ceiling was insulated with foil-backed fiber glass and finished with ceiling tile. A friend advised that the ridges were formed expansion and no cause for concern. In the fall, however, the ridges were still there and had become brittle. I closed a broken one with patching material. What causes such bubbles? If resurfacing is needed, how can I prevent recurrence?

ANSWER: By converting your attic space to a finished room with the installation of fiber glass in the roof rafters, you apparently did not provide any ventilation between the soffits and the ridge. Previously, the attic was ventilated.

A dropped ceiling for the attic would have been preferable since you would have maintained some air space above the ceiling with the added ventilation by means of roof louvres. Now, you may have to check the southern exposure of your roof to determine whether it is still bubbling. Your action with the patching is satisfactory, although temporary. You should install roll roofing with white granules, which may be covered over with the salvaged slag. The reflective quality of the white granules plus the white slag should be beneficial. As for resurfacing, check with your roofer.

DEAR SAM: How can roots embedded in the stucco of our house be removed? We have cut off the English ivy but find that the remaining roots cannot be budged with a wire brush or by scraping. I hope there is a method to disinter these tiny roots without damaging the stucco covering the cinder-block walls. If this is not possible, shall we just paint over them?

ANSWER: The roots have penetrated tiny crevices in the stucco or cinder-block joints. Since you have undoubtedly cut the earth-bound roots, these roots will eventually dry up.

Your painting need not be deferred. I recommend the use of exterior acrylic latex in the color of your choice. A slight sandpapering of the crevices should make these areas quite smooth; also, the paint will act as a filler to conceal the spots substantially. When at some future date, you decide that a touch-up is worthwhile, the leftover latex paint will blend in.